it's not as easy as you might think.
first you need a bmw air conditioning compressor that fits the n54 mount and has a magnetic coupling.
these compressors have a 6-fold strap. the n54 has 7-fold strap. This means that you then have to choose a suitable pulley with 7x that also fits on this compressor.
then you have to made a suitable shaft that connect to the hpfp and the magnetic coupling.
last but not least, you need suitable high-pressure lines.