There are already a couple places where the engine is grounded. I would say that if you are having grounding problems, find the ground straps, and either clean them up really well, or just replace the straps.
'86 325es (TURTL3): PJ peetsa hawler
'87 535is (BADWATER): almost done... really.
'86 325e (GRN HLL): DD/show/rocket
'04 x3 3.0i: Wife's Bimmer (manual, woot!) My BMW Blog