ran into the same problem but in reverse with my blades. Knew I would be getting a drysuit when I bought my gear so I went with the large. they fit ok with my 5mm boots with just a little slop. Fit like a glove with the drysuit. However as they got used more and more they became a little sloppy with the 5mm boots. Do not have any use for 7mm's so I shopped around and waited. Sure enough another pair of used blades came up on ebay for 12 bucks and I snagged them up. They were also a large but the old style with the tapered foot pockets. Wider at the front narrower at the rear. They are perfect with the 5mm boots. That may be his option. Find another pair of fins that fit well with the 7's and switch between the two. I realize this may seem a bit excessive given the cost of the split fins but it may prove to be cheaper in the long run in terms of comfort, fit, wear and tear on the foot, and it's always good to have extra gear. I actually have 4 sets of fins. 2 open heel for scuba, 1 full foot for snorkeling, and 1 for pool training. The pool fins are inexpensive full foot ones that force me to kick harder and faster and give my legs a good workout and have increased my stamina and power with scuba fins. You also did not say what size feet he has but I'm not sure the foot should peek out any holes. They may fit like a glove where on dry land? He should try them in the water for a while and as Mark said see if he can try em with a set of 7's. Again preferably in the water. I had to exchange my first boots cause they felt fine out of the water but once they got squishy in water they felt like they were falling off my feet. Turns out they were! This could also affect fin fit. In the opposite direction if the boots are too thick for the fin you might as well stick your foot in a vise for an hour.