Just put floats on it and land on the lake.

The drogue chute would be a nice effect, you could rig the servo that deploys it to release it in case of emergency. Would be a nice effect, but don't know if I'd want it on a trainer - would be a disaster to accidentally deploy it in-flight.
If you are running the ailerons with two servos on separate channels (can't do this using a Y-cord), see if the transmitter has an airbrake function (both ailerons up, elevator down at the same time, I think). That will give you more drag on landing.

Seriously though, if the grass is cut short enough, landing in grass instead of on a hard surface would slow it down a lot faster. If you are already using a grass landing strip, go with the smaller wheels.