Revisiting this old thread, finally saw the E70 in the flesh here last night at the dealer launch. Both anchor points on the 3rd row seats have a release button so both lower attachments of the seat belts can be released and stowed away as pictured above.
I wonder if it is a difference in the EU models but it works great. Will take pictures when my car is delivered.

C

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X5 3.0d few essentials June delivery