Get you a truckers Atlas and plan your route.  When empty I would drive on by.  When you are loaded coming back I would drive 10-20 miles out of your way to go around the scales.  The one at Indiana can be gone around and the one in MO can too.  I've avoided the one in IN, I presume the one on 36 by St Joe is the other one, I've always gone across it, but have heard it can be missed.

If your truck and trailer has a GVW of 26000lbs or over you might need a trip permit if you are in a diesel pu.  The farm plates will help, I would go pick up the equip and avoid the scales on the way back.