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I can think of 2 things to try. If you can get access to the positive post of the starter you could hook a battery charger to it, charge the battery, then use the trunk release or perhaps using one of those battery chargers that hook into the cigar lighter. Or possibly if you have a B+ spot on the fuse box that is accessible, but before that if it comes down to that, I would first like to see a wiring diagram.