I think I've figured out how to copy scores onto letter-sized paper relatively painlessly.
Hit the following buttons:
Once you put the score on the copier, it should read the size of it and reduce automatically. (This might happen after you ask it to copy once. I don't really remember.) The last score I copied reduced to something like .964. I did have to figure out how to place the score on the glass to get everything, but there is a handy ruler on the side of the glass which you can use to duplicate the placement, and this at least takes the guess work out of the reduction.
Finally, I think we've figured out the proper purpose of one of those mysterious and annoying extra functions! Yay!