I would like to be able to put blocks of text in a document that don't affect the layout of the main part of it. (Specifically, I'm writing the solutions to a previously written exam; I'd like to be able to add the solutions in without causing the text from the original exam to move around.)
For what it's worth, the original spacing was largely handled via "\vfill", and I'd like those to still take up the same amount of space. (In principle, this means that if a solution were too long, it would run over and end up on top of the next problem, and I expected to have to manually check that this doesn't happen.)
Update: Here's an example, except that it isn't doing the spacing quite right. (The stuff in typewriter font is the solutions.) The point is that I want to leave the spacing of the original exam content alone, while inserting the solutions---complete with formatting---in the gaps left behind. In the unlikely event that there isn't enough space, I expect that any solution might cause crazy things to happen, but I'd like the typical case, that my solution fits in the space allotted, to be relatively seamless.