depends on if these things also simulate the readyness status, because I believe thats all they check..

would be pretty easy to detect you had it wired in there, because speed, rpm, time since start, etc will all be obviously wrong if they decide to look at any of those values..  but then again you could get some kinda electronic potomoter and do some nifty electrical engineering hacking the hell out of it to hook outputs from your standalone into the simulator, and out the OBDII protocoll.. hrmmmm

I have gotten an OBD2 ABA ecu to have no codes on the bench simulating but it was a whore. There's no way I can make it pass readiness or do anything else. Shit's too smart and without recoding the shit out of the ECU that's about it for me.