All you have to do is PROVE explosives can survive the impact of the aircraft and subsequent fire.
One should be careful playing games like this. I'm a Mech Eng and this is merely a technical problem and one that would be likely be easy enough to solve.
One could for example simply encase the explosives in a thick steel case lined with a very good insulator, like that of the shuttle tiles
http://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system
some would get destroyed by the impact but most would not and all they would have to do is survive 1 hour of fire (in the case of WTC1 and 2.)
Even setting them off wouldn't really be a problem as they could simply have synchronized multiple timing devices. each charge has say four timers and a circuit that won't set of the charge unless 3 of the four timers agree.
so having charges that survive the impact and fire is a mere technical problem and one that any half competent engineer could solve given time and money. The engineer might not even need to know what the application is, just the design requirements.
However that would not solve the problem as to how they would install all these hundreds of charges, all without anyone noticing AND leaving no signs afterwards that the beams were cut and no signs of the charges and their enclosures and timing devices. THEN ensuring the dozens (hundreds?) of people that would necessarily be involved in just that phase alone, all keep quiet and stay quiet.
Anyone presented with such a plan would simply say "wouldn't it be simpler to just con 19 religious nuts to fly planes into the towers etc and let the uncontrolled fires take them down? I mean didn't the hard fought Meridian fire nearly take down that tower? and worst case even if they stay up we still have a terrorist attack that is more than enough excuse to invade some desert place that doesn't have any oil?
Twoofers like the CD idea just because it is so complex, this is just a symptom of their affliction not a requirement in a real mega evil NWO, shape shifting lizard, Illuminati or Wombles plot.