If you've already got a system that doesn't involve switching the pins, awesome. I also thought of traditional relays or SSRs. You can pick up 12v automotive relays on the cheap from junk yards, just make sure you can test them there and don't forget the flyback diodes. A 9v once across the right terminals once shouldn't pop them right off. There are also known footprints and CAD models for them. A good choice all around except for the constant current draw one way.
I didn't mean to make it sound like an insult and thought I'd point out some things to watch out for. I had something better typed out but I refreshed and lost it. Repetier has an online config tool with diagrams, it's pretty sweet. Have you looked into the hyper cube?