When I first read this post I thought of the microsail site. Was going to post a link but was beaten to it
A spinnaker on a model yacht is way cool, but a lot of trouble.
I guess an asymetric design would be best. One winch for up and down and one for control. A bit of work would go into it, making the downhaul and uphaul work off the same winch could be a challenge. Same said for the control winch. But hey if someone wants to give it ago I'm willing to watch.
P.S I aslo sail fullsize. I sail a Cherub.