FT -- the answer is No and Yes.

No: Your MSL-MSR (multi-function switch left and right) uses CANBUS 2.0b to communicate with the console to control the turn signals (the MSR uses wires to communicate cruise control switch actions to the MSL which then uses CANBUS to inform the console, ECM, etc). The MSL periodically (about every 200-300ms) sends CANBUS messages (340h 11-bit identifier for my CANBUS 2.0a Spyder) about turn switch press status: Left, Right and Center. I suspect the console waits for two consecutive messages with the same status value (0 or 1) to "debounce" the press (Left is word 2 bit 7, Right is word 2 bit 6, Center is word 2 bit 5). Therefore you can't override the MSL by injecting your own conflicting status messages on the CANBUS because the console wouldn't be confused -- it would just ignore them as transients to be debounced.

Yes: take the turn signal function away from the console. Not that hard but not for the timid. I'll say more on this in the near future (right now my Spyder looks like a rat-rod as I drive around without the bodywork).