when the trainer switch is held down, the signals transmitted are from the slave transmitter (the actual RF energy is coming from the master of course). In other words, all the fancy settings in the 662 are ignored. If you have expo or dual rates programmed in the 662 there is no way to use it from the slave transmitter. No workaround that I know of.
Of course, you can change the mechanical linkage (put the clevis on a hole further out from the hinge line).