I bet it can be done. Last fall one of the local dealerships had a 47 row 15" planter in and I seriously doubt that the owners were planting 15" corn. Technically you "should" be able to block up the intermediate rows and disengauge the drives. Local dealer has a 54 row 20" planter in I guess. I'd like to see that.

I don't know about planting wheat with a Deere row unit. Don't know that you could even create enough vacuum to do it with the standard two motors.