The analog outputs on the AT-MIO-16E-1 are setup for voltage, but you could set generate a related current with external circuitry. This is not a trivial task. If you need to source current, I would recommend using the NI-6704 or a signal conditioning solution. More details about the 6704 board can be found at:
http://sine.ni.com/apps/we/nioc.vp?lang=US&pc=mn&cid=1100
The signal conditioning solution I would recommend would be the 5B39. More details about the 5B modules can be found at:
http://sine.ni.com/apps/we/nioc.vp?lang=US&pc=mn&cid=3246