If already glued and riveted, your option is to buy the parts to make a new rudder.
I used a piece of angle iron, perhaps 2" by 2", as a means to hold the trailing edge to the flat (and sturdy) table top. With the trailing edge glued and ckekoed, have the edge just hang over the edge of the table so the clekoes clear. Put the angle on top of the trailing edge resting on the clekoes. Take a 25 pound bag of lead shot and put 5 pounds or so in zip lock bags. Put the bags on top of the angle and extend over the rudder (or whatever control surface).
Let the glue set, then go back and rivet.
Carl