I know I did it on my e39 without a problem. I had to pull out the underbelly pan to reach it. It's between cyl 5 & 6 if I recall correctly. I used a wobble adaptor & extension, no problem. My X5 is the 4.4, so it's a different layout but for all intended purposes, once the steel plate is out (which is not hard to take off), you should have a clear shot at the drain plug. I just finger tightened the plug for the next 3-4 water flushes (garden hose), kept the heater core hoses on/off as I filled/emptied the system, and also used compressed air at very low pressure. Once the fluid stopped coming out, and I used the compressed air, another 1/2 - 1 qt of fluid would squirt out.
Really easy once you get in the groove.

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Stable: e92is, e46 M54B25, e83 N52, e53 N62 - sold, e39 M54B30 R.I.P.