A set of switches on the side car will get the job done. Since there is no interaction in auton, there's no reason you need to wait until your opponents place robots to decide your autonomous mode, the main reason to put the switches on the DS.
You can use a simple binary system to get 2^x auto modes with x switches. Or if you want to configure something in your auto mode, you can use a few switches to set a value from, say, 0 to 15. No idea why you'd want to do THAT though...
