I'm good with that - mid way or at the rear 2/3rds area approximately has been my observation
You can add them once the driveline is on the car (just have someone rotate the rear wheel) or build yourself a fixture that will hold and let you paint around the whole driveline without stopping in one shot. Have seen guys use old roller skates, skate boards or what every. Good time to get one of the kids or wife involved spinning the driveline
I've also used to sections of 2x4 screwed to a section of plywood to keep them in place and on their short side. This creates a moving driveline as you roll it across the 2x4's but is quick and not to fancy if your only going to do this once. Practice with rolling with one hand (or fore arm) while you hold a dry brush against the driveline for one fully (plus a little) rotation.
This takes a bit more skill and effort than the roller ideas