Nope.

Not possible.

Well, almost anything is possible, but there does not appear to be any practical way that I have seen or read about. The ability to turn off the monitors is probably a liability and/or legal issue, as I suspect since they are now a Federal legal requirement, the law probably does not allow for the system to be able to be turned-off by the user. And we've seen an example of someone's child accidentally turning on the hourly chime function recently, so a BMW lawyer would likely be rather worried about accidentally turning off the TPM system.

I suppose you could carry the original wheels around in the back.... just kidding.

I believe Tirerack sells compatible TPM's, and if just for safety reasons, it's probably a good idea to spend the extra $200-300 to keep the system active in any case.

P.S. A quick check of tirerack.com shows that the X5 TPM sensors/valve stems can be bought in a package of 4 for $196.00