J, I find this hard to believe.
the DME Should be able to control the fuel pumps w/o issue as long as there wired in correctly
an AEM infinity-10 (miles ahead of the Motec offering) is about $3500 and it Replaces the BMW DME...Tuning it is NOT 5K and a custom wiring harness is also not 2k
so yes it can be done.
we have done it on the S54 M3 and the S65 Platforms...i think no one has tried it for the S85 platform but its not very different
Question for the OP is why do you feel you need a HP fuel pump? just upgrading the fuel pump alone wont help much until your certain the injectors can flow more.
whats your goal or thought process behind the "why"?
A bit OT, but why do you feel the AEM is superior to the M1 series? AFAIK, there hasn't been a single S85 run on the infinity yet and only one S65 under development that I know of. AEM hasn't announced an "application" yet for either engine and aren't really keen on opening up the development software for anyone else to do it. At least with the M1 series, M1 build software, and a development license, you can program whatever you like.
I've been researching standalones for the S85 for a couple of months and have looked at ViPEC, M1, AEM, MS3, as well as modifying the mss65. So far I keep coming back to the M1 since it has the greatest potential to eventually make use of the ionic control and oil sensor as well as an already established S85 history.