Go here:
http://www.healtech-electronics.com/Buy the SpeedoHealer.
Install as per instructions.
It fits in-line between your speedometer sensor and your ECU and changes the number of pulses your ECU sees.
I needed one on my Sport 1000 after switching to 999 wheels (5 bolts instead of 6). Installed in an afternoon and now I have a better idea of just how badly I'm breaking the law.
The most difficult part was verifying just how off my speedometer was initially. I had a friend drive ahead of me on the highway and go as close to the posted limit as possible, then made a mental note of what my speedometer indicated. Plugged those numbers into the calculator on their website, got a "correction factor," plugged that number into the unit, and tested again later that day.
In retrospect, using a GPS unit or a phone app that records your speed would be easier, and probably more accurate. Oh well. I'll know for next time.
Post up when you do the swap. I'd like to see that, and I'm sure others would as well.