I've found these nifty little [link=http://www.sonictronics.com/products/hinges/prod03.htm]dummy hinges[/link] from sonictronics.

They are stiff plastic hinges that are temporarily put in place instead of CA hinges while you shape and sand the control surface. They work pretty well.

Of course, if you're not using CA hinges and using Robart hinges, you could just substitute the hinges with wooden dowels while working with the control surface.

Hope this helps...