You could modify the formula with Sheldon's advice. Air up to 67/60 psi then check to see if you have a slight bulge when you sit on the bike. If so, that's probably about right. If it seems low, add 10 psi and check again.

Running the formula to see what rider weight it would take to get to 110 psi for a 32c tire comes up with a 402 lb rider! Yowza.

As always, YMMV.