In the late 70ÃÔ I bought a suit made with out of (nitrogen expanded) silicone rubber rather than neoprene. It was made by Imperial Turtle and they called the material Glowflex.
The rubber was laminated on both sides with nylon fabric, just like most wetsuits now a day. Most edges were finished in a way that you didnÃÕ see the rubber material, but in a few places you could see the bright orange silicone rubber material.
My wet suit was a two piece (all wet suits were two piece back then) farmer John bottom, beaver tail top and all the material was 5/16 thick. It was still very flexible as compared to other suit at the time.
The suit was great, but I outgrew it a long time ago. I wish I still had it.
I donÃÕ believe anyone makes anything anymore with anything but neoprene.
I would think that using a skin suit under the wet suit, in combination with the nylon laminate, it should isolate him/her enough. I would try some rental suit, just for test purpose.
Another suggestion is to call some of the large wetsuit manufacturers like Henderson and see if they have any recommendations. They might have run into this in the past. Henderson in particular has several different suits with different interior coatings. They may have something that would work.