How about a pair of these for the trunk BP?
Officially called the BMW Oil Travel Case, PN: 83 29 0 144 484. I carry two in the ZHP, though we can get BMW antifreeze in quart sized bottles which would fit too, I believe. Cost is $5.95 each, and the velcro nicely to the trunk lining.
If this doesn't spend enough $, how about some additional antiseize compound?