sorry bro. misread your enquiry. As I dont own a Z4, I would not be able to answer your question.
Presume, the easiest way is to buy a seperate jack and proper tool to release the wheel bolt. For my E46, there is a smaller size emergency wheel that can store at the rear that allows a max speed of 80 Km/Hr.
Just a question. Why are you converting back to NORMAL tyres.
Is the RTF no good in term of handling, performance or it is just too expensive?