I don't think it will work. Pearl gourami need a larger tank. A 20 gal long is only about 30 inches wide. Pearl gourami need a 3 foot tank. And like all gourami, they will get aggressive when they breed, and the males are territorial. A better gourami for that tank is the honey gourami. You could easily keep a single male and two females in there. When you keep gourami in pairs, the constant pursuits of the male can stress a single female out. It's best to give the male options so he can spread out the amorous pursuits.
If you just wanted a single gourami, you could go with a thicklips gourami or banded gourami. They are larger, so a group wouldn't work in your tank.
I think I'll go with 3 honey gouramis then. Thanks for the input! :)