For many years off and on I flew planes with engines that had no throttle. 1/2a being the most common. But I flew planes that used as large as a .36 engine before too. Only rudder or aileron and elevator, no throttle. I remember guys flying large .60 size planes with no throttle before too, but that goes way back though.
For pylon racing we used to use a fixed fuel pickup, no flexible clunk in the tank. You would simply go inverted for a few seconds to kill the engine.
Trainer types of planes are harder to do it with though, You usually wind up doing a 1/2 loop and hold the plane inverted until the engine dies. of course you get the plane up high before you do so.
Then you just perform a dead stick landing like normal.

So if the original poster does not have a throttle try a fixed fuel pickup and going inverted for a few seconds to kill the engine on command. If you have a extra RC channel, you can rig up a free flight fuel cutoff too, and control it with the extra channel servo.