This isn't exactly a foot control, but it is simple and easy to rig in a flash with no alterations to your boat:
Note -- this works with the new style rudder controls. This installation is on a Revo 11.
The PVC slips over the rudder control (part of the PVC bottom is cut away), locked in place with a hand-tightened screw into the threaded area in the handle. The end of the PVC is angled to fit your leg (hint -- use hot water to shape the PVC as necessarily). Industrial strength Velcro is wrapped around the PVC and your leg -- sticks enough to manipulate the handle extension with your leg but breaks away in case of capsize.
This doesn't give you full rudder control, but turns the boat effectively in large sweeping turns -- should work with your paddle. On the Oasis this might work out best in the narrower front cockpit, which is also probably the better location to paddle from.