Interestingly enough I asked the same question to Kenwood to see what they would recommend, this was their response:
"To use your existing infra-red remote, you can use either KDC-BT92SD, KDC-BT73DAB or KDC-BT48DAB
These models have infra-red sensors, but you may need to alter the position of the infra-red transmitter (located above the stereo location) because the infra-red sensor on the front panel of these models may be in a different position from your existing stereo. Additionally, the front panels may be thicker than your existing model, so you may need to bring the infra-red transmitter forward.
Unfortunately this can only be done via trial and error.
The other option is to abandon the use of the infra-red transmitter and go for a hard-wired steering control interface such as:
CAW-RL2001 with either CAW-MG2033 (ISO) or CAW-MG2034 (BMW)
All of our BT models have facility to connect to the hard-wired adapters
http://www.kenwood-electronics.co.uk/products/car/cd_receivers/bluetooth/
BT models that stream music as well as hands-free calling are:
KDC-BT92SD
KDC-BT73DAB
KDC-BT48DAB
KDC-BT44U
KDC-BT34U"