Clever! Funny - I would be more scared about putting whiteout on one of my "black beauties" than sticking down tape but I'm glad it worked out! I wonder if a Command strip would work...
I have a few of the metal guides that screw into the bed of the machine; haven't tried to see if they fit my 99's or not though. I do better with a physical edge to butt the fabric against; a line is too easy for me to ignore, LOL.