MINIzguy: Not a great idea. The circuitry is still there to charge the battery and so your non-rechargeable battery will be getting charged every time you drive. At best it will probably leak eventually.
mraghvani: If the keys are truly blank, you can program the key using a special device (an EWS programmer can read/write keys and the EWS). However to program a key, you need to pull the EWS out of the car to get the codes to program into the key. EWS programmer is about $150-200 and is not a BMW tool.