Having stumbled across the surplice neckline for catsuits, I determined to try to find a similar pattern that worked for zentai suits. I think it was a forum discussion that suggested some sort of overlap.
I tried a few locations where an overlap would have worked - along the spine, around the back at waist height - but the best place seems to be the shoulder region: the waist height overlap was really hard to get into and tended to gape open, while the back overlap was really, really confusing to sew at the bottom, and tended to gape open too.
The basic strategy for these suits, then, is this: Take two basic zentai suits. Cut the top off one suit from armpit to armpit and discard the body, to make an insanely high-cut T-shirt. Cut across the chest of the other suit from armpit to armpit. Sew the high-cut T-shirt to the lower-body side of the slash so there are two tops on one body. Pull the suit up to your chest, slide your arms and head into the back top, then pull the front top on too.
Of course, rather than actually cutting up suits, it's the patterns which are modified.