Your fantasy construct will do fine.
My wish is your command.
Conspirator 1: There must be a hundred tons of that nanothermite paint stuff on those pallets of barrels. How are we supposed to plant that in the Trade Centres without being seen ?
Conspirator 2: We've developed a sweet little system especially for this, See these core columns cooloured red on this plan ? Well we're poing to pump this stuff in right INSIDE those selected hollow columns. Thev've all been sealed...no holes anymore. We may have to even fill them right up as far as the 88th floor or so.
Conspirator 1: At night I suppose ?
Conspirator 2: Mostly I guess, but we could do it in the day too if we want, You just have to have those paint tanks on wheels full of the stuff. You wear overalls like maintenance guys and if anybody asks what uou're doing you just tell them it's to do with the fireproofing or painting or cleaning or something. It's only a matter of inserting a tube into a specially drilled hole and get pumping. Nobody will notice a thing.
Conspirator 1: How will they spark it off then.
Conspirator 2: programmable Electronic detonators and redundant relays all over the place. No sweat.
Conspirator 1: Speak for yourself boss. Me and the boys will be the ones dragging these things around.