I agree with you,
I’m all for dynamic EMS use, i.e. EMS with full movements. As a matter of fact I’ve listened to a lecture at the National Strength and Conditioning Association symposium, 2007 (Atlanta) which comparing static to dynamic EMS, showed better results for the latter (this was a study on diabetic patients, but I suppose the results apply to athletes).
I’m not a sport kinesiologist, but IMHO if you do not have the possibility of using a legg press with EMS, to train for jumps one could pick the position that develops most power.