I bought the SM10 Bluetooth dongle from Motorcycle Dave. I was also installing a sport rack, so I killed 2 birds with one stone. I had to remove the seat and passenger grips, so I didn't have to remove the entire side panel, which would have been a real pain.
I rode a couple times this week and tested out the system. I have Sena 20s headsets, and they sounded great with the Bluetooth. Last night my wife and I rode out to dinner and the dual stereo function worked beautifully.
By the way, I was going to put the SM20 under the seat, but then decided that it would be more practical and accessible if I used the handlebar mount and put it on the passenger grip. I'm not sure that will be the permanent location, but it seems to work well. Other suggestions would be appreciated.