Welp, I guess there's only one way to find out. I'm just finishing up a drawing for a antique'ish 3 channel model. I think along with the tip dihedral 3 channel wing I'm gonna make me a second set of feathers with spoilers for roll control but keep enough dihedral in there that I can at least get the kite back on the ground if they don't work. And I think I'll make them multi paneled so I can try the size and position.

More in a couple of months. Dipsy, I'll keep you in mind and PM ya when I have some real world results.

In the meantime here's a sketch of the cargo twin I want to use the spoilers on;