I would just run one off the herpstat and then have the other thermostat run on its own the other rack. I wouldn't have the 2nd thermostat running off the herpstat.

As for temps, 88 is too warm for cornsnakes. Aim for a hot side of 80-82 and a cool side about 8-10 degrees lower. I used to have both in one rack, when I only had a couple of ball pythons. I never had a problem keeping temps correct in their cages.