Basically as Pete says - You're stuffed. Pre-Roadster are free of such encumbrance. Roadster and iirc the T have CANBUS. This requires a decoder (basically a very simple computer) in any device connected to intercept, decode and re-emit signals in the BUS.
The only real option would to be relocate the original speedo somewhere hidden and connect up the Dakota using an alternative speed sensor (GPS would be an idea) - But without the ORIGINAL speedo connected the CANBUS bikes will not start. Until some electro-genius comes up with a CANBUS fooling device.
Worth noting that with Euro5 - there comes an obligation to use OBD2 on M/C. This means the use of GENERIC OBD2 devices. The R3 has OBD1(and a bit). There will however be other encumbrances to individuality.