You could swap/transfer your TPMS sensors from your OE wheels to your aftermarket ones. I think you will need a special low torque wrench though. Something like ~7Nm(???). Its very easy to over torque the valve stems and break them though. I would have a German tire shop do the swap.
Brand new TPMS sensors aren't that expensive though. Back in 2010 they were around 45 euros each. I bet the price has dropped a lot since then. I would stop by a BMW dealer and ask.