Bipod Drawbot

I'm working on a Drawbot, a Hector clone.

So far, I have 2 steppermotors that I can fully operate using the Make Controller and processing. The whole thing is set-up, and I can do some basic up/down/left/right movements right now.

At this point I'm using all of the Digital Outputs from the makecontroller for the steppermotors. But I still have to implement the pen up/down.
How can I fix this? Can I use the servo outputs somehow? Is there a servo motor that can do an in/out movement? Or can I use a electromagnet somehow? Or something completely different?

You can find some pictures of the project at this flickr set

you might consider using the servos to move the pen up and down like piston/crankshaft type setup. if you have a little tube you could set your pen up in, then connect the rear end of the pen to a servo horn. Just rotate 180 degrees for an up-down motion.

It sounds like the simplest thing to do would be to either use a servo horn to push the pen down a spring-loaded slot (or use a two-prong horn to grip it above and below some point with a little rod glued on) or just use a pull solenoid to bring it off the surface (you can drive it with a relay or a fet).