If in doubt, check the laws in your state, regarding signaling for a lane change.
I always try to give my lane change or TURN signal as far in advance of the motion as I can, to give the other drivers behind me plenty of time to see my signals.
Even then, they sometimes ignore me and pass me while I'm wanting to change lanes.
This has been asked a few times before and people have speculated that the dealer may be able to do this on vehicles that don't have the cluster that lets you do it yourself. Nobody has reported back recently that they've asked the dealer to try, so if you do ask please let us know what happens. I'd like to do this on my + too... forgot to ask when I was in there last week.