generally speaking you'd need to retrofit the brakes to something with a manual cable actuation in addition to electric. The electro-magnetic only brakes can only be actuated by continuously applying power, which would result in a dead battery fairly quickly.
Thanks SBSYNCRO! I wish I'd seen this a couple of years ago. I didn't know they make a combo manual/ electric brake. But, I am looking for a solution that I can add something to what I have now. But $255 is not too bad.