I wonder it the RTI controls could be just relocated a little further rearward or more underneath the wheel. The RTI switch is somewhat awkward to use anyway.
It will be interesting to see how the paddle shifter works exactly. It would likely be one of two ways.
One way would be to tie into the control bus with a digital signal. If this is the case it might be possible to tie into the bus at the RTI controller. This would piggy-back the path that wiring is taking from the center of the steering wheel into the column.
I suspect, though I haven’t taken mine apart to see, that the center console shifter is nothing more than two momentary switches, and the steering wheel switches just operate in parallel with these switches. If this is true, then it would be a matter of mounting two switches on the steering wheel, and running two pair of wires from the steering column to the center console, and tapping in to the wiring at the console switches. This theory could be tested by splicing a couple of momentary switches from Radio Shack into the center console wiring and then test driving to see if the temporary switches performed the same function as the console switches. You could also determine whether the shifter needed to be in the manual gate before the + – switches work. In the S60 I recently drove, the paddle shifters operated on their own, independently of the manual gate position. I believe though that moving to the manual gate portion activates a slightly different engine/transmission mapping that is more aggressive. If this works, then any momentary switch could be mounted to allow manual shifting.
Another possibility: I previously owned a G35, and a very popular upgrade was to retrofit paddle shifters. They are available as kits (search on “g35 paddle shifter”). The G35 paddle switches alone are available without the rest of the kit. If the momentary switch indeed works, paddle shifter like these might be adapted. The difference would be that these paddle shifters would mount on the column rather than the steering wheel. (I actually prefer this as often when in mid-turn its difficult to find the switches on the rotating steering wheel, where the column mounted are predictably in the same place). Of course the spacing would have to be right for it to fall-to-hand.
Its a shame that many car companies are reserving these paddle shifters only as an option on the higher priced packages. The Ford Focus and Chevy Camaro rental cars I had the past two weeks both had them on some pretty basic packages, and many economy cars now do. With many of the controls now being electronic, this is very cheap for the manufacturers to provide.
While on that subject, I also find it interesting that Volvo does not offer certain options as affordable dealer upgrades. I would think that availability of options like paddle shifters, back up cameras, NAV, BLIS, etc. as common dealer installed options would be a profit center for many dealers, and facilitate sale of certain used or new cars where having these options I would make or break the deal. While some of these are available, they are cost prohibitive.
Nevertheless, keep at it and let us know of your progress. If you can accomplish a paddle shifter retrofit for the kind of money we are talking about, you will be very popular. 