I ended up using some strips of rubber bonded to the heel (mostly, 'cause that's what I had lying around, scavenged from a stage bottle hose retaining band that had seen better days.) It worked very well; the rubber of the spare innertube bits on the heel was pretty good against the rubber hose that I use on the spring straps. I may still try to run by Value Village or something this week and see if there's a cheap pair of shoes to cannibalize, though this was quite good.
The adhesive didn't fare so well. I used seal cement, since that's what I was using for the other stuff yesterday (putting a pocket on one of the other drysuits I have...) Four coats to soak into the neoprene still left the edges peeling away. I was going to try running some seam tape around the edges to keep them from lifting, but I think I'll move to Shoe Goo, or one of the similar, tougher adhesives, first. The seal cement might be fine for pockets and wrist/neck seals, but it can't hold up to the abuse of the spring straps.
Still - a worthwhile experiment. Way better than the stock turbosoles, but it'd be much nicer if DUI returned to the old-school boots they had years ago. One piece, on the suit, with suitable heels/toes. My two Andy's suits and my Diving Concepts suit both have excellent boots (particularly the DC), but I like my DUI suit more...