A misattributed text seems like a different animal, and we know now that, in a sense, all alchemy texts are "fake." But I don't think these count as "prop texts" in the way we mean here, with the secret writing and all.
I cannot think of specifically this kind of prop book being used, the Voynich is indeed unique. But then, the other explanations offered for its creation don't seem to have other similar examples either. And it fits a pattern that frauds and imposters have used through the ages. Pronouncing magical formulas in a made-up language for instance, could be thought of as a verbal equivalent, but much less laborious to produce. Simply reading out random Latin texts pretending they're magical incantations of some kind, knowing your audience doesn't know any Latin has also been known to be used. And of course, in more recent years, there are plenty of examples of fake supposedly scientific devices, usually with medical purposes, for instance just boxes with some knobs and switches on the outside, and some wiring and maybe some electronic components inside, that do absolutely nothing. Those fake bomb detector devices (as used in Irag), also sold as drug detectors, are another example. Those could be thought of as a sort of modern-day Voynich-as-a-prop equivalent: something designed to just *look* like it might be an actual working electronic device to a gullible layman.
Somewhat tangentially, I can think of two examples of 'prop books' with meaningless or no content being used to deceive the public, but innocently.
One is the tradition of Sinterklaas (St. Nicholas) in the Low Countries. When Sinterklaas arrives from Spain, by steamer of course, he brings with him a big book, which has the names of all children in it, and whether they have been good or bad that year. If they've been bad, they will be punished by his servant, Zwarte Piet, otherwise they'll get a present. So it's part of the ritual of some Sinterklazen (to use the Dutch plural) to ask children their name, then either ask Zwarte Piet to look up the name or ponderously consult the book himself. Mysteriously, it always turns out the child has been good and gets a present. Of course, in this case most of the target audience is too young to read, and never gets a good look at what's on the pages, but it needs to be a big, impressive-looking bound volume (after all, *all* children are listed in it). I've seen several different books used for the purpose. Large-format Bibles do very well, as they also often have a cross embossed on the front, which matches the one on Sinterklaas' mitre (sadly, some Sinterklazen these days use crossless mitres, which just isn't right). But I've also seen big dictionaries (language irrelevant) used, and on one occasion the collected works of William Shakespeare. As long as you cover up too-obvious words on the cover, and it looks as though the pages are covered with lots of information, it works fine.
The second example is the signing of the Treaty of Rome in 1953, which formed the European Economic Community, later to evolve into the European Union. The treaty was actually negotiated and agreed on in Brussels, but for symbolic reasons the official signing was to be in Rome (very consciously to bring up associations with the Roman Empire). The problem was that the time between the agreement and the signing ceremony was so short, the Italian state printers who had to produce the lavish bound presentation copies of the treaty didn't have the time to typeset, print and bind them. So what they did was produce essentially blank books, except for a title page, a page with a hastily-written "Preamble", so the books could be opened to those in front of the cameras to pretend it contained the treaty, and the pages at the end, where the signatures of the six heads of government would go. So in the footage where you see those "treaties" being solemnly opened, presented to each signatory in turn and passed around until everyone has signed all the copies, they're all signing shams, just a bundle of blank pages. (The real treaty existed only in a typewritten version with carbon copies.) I don't know if they later produced versions with the actual treaty in it, and discreetly sent them round the member states for a second signing, or what happened to those original empty versions (maybe they simply unbound them and replaced the blank pages with properly printed ones). But what if hundreds of years later, someone with no knowledge of how this came about or about the general historical background, found one of those original books: a title page claiming a "Treaty", a vaguely-worded preamble, and then hundreds of blank pages, except for the last few pages, which contain the names and signatures of six heads of government, wouldn't he also think he had a major mystery book on his hands, instead of an innocent prop only intended to look like a treaty for the cameras?
