Here is the proposed solution from mods4cars (hopefully someone can translate this into a DIY for M3s...):
"Solution: Disconnect the power wire from the thick red power wire to the top control module (smartTOP) or the radio (smartTV) and connect it to an unswitched (Terminal 30) wire, directly to a fuse powering a Terminal 30 circuit, or run a wire (with inline fuse!) directly to the battery "+" terminal.
We recommend getting a ~6ft long power wire with 1 or 2 Amp. inline fuse, available in car accessory shops for example to hook up radar detectors or CB radios."