[celsdogg]

you might be outta luck.

Usually controlling speed in this way in a MT is because the throttle plate is closed and causing a vacuum behind the throttle. Turbos increase pressure (thus the reason we have vacuum pumps) but more pertinently, BMW keeps the throttle plate open and control engine speed with the valves (valvetronic). There is very little ability for the motor to control speed during deceleration. It still drags a little, but no where near what you need for a long steep downhill. I am not sure what the answer is to prevent overheating your brakes in those situations.