I spoke a little about this in the 3rd & 4th paragraphs of this post. So you can see the logic behind the point about "paritioning" the HD20. However, despite having read that Nested Volume Manager article, I am not sure how to do the partitioning myself. But if someone could enlighten me on it, then I can try to reformat/repartition my HD20 while at the same time try an MFS partition along side some HFS partitions. But to make the entire disk MFS would be rather nasty (e.g., in Open/Save Dialogs) in light of MFS being a flat file system, especially if you have a huge number of files on an HD20 like I do!
Kudos to Mac128 for solving the 800k MFS issue!