There is still yet another potential-100% thing that I haven't checked, but it is definitely a glitch, so it doesn't sound like something that guest did.
I did a quick test on this on the PC, using a custom-made level to facilitate specifically the testing of the idea. Results indicate that it just doesn't work.
So I've certainly exhausted all my far-fetched, potential 100% ideas as not working (much to my gratification in a way, since they would otherwise defy my understanding of the game mechanics). Until some new glitch is discovered, I don't think 100% is possible with the amount of skills you're given.
(And I haven't received any e-mails from guest yet so currently there are no new inspirations or ideas for new glitches either.)
I still appreciated guest's attempt on this. At least he seems to have gotten either to where I am or very close, and it was stimulating enough for me to check 2 possibilities that I didn't check for earlier, even as they turn out fruitless. B)