I used this old Black&Decker jump starter that fed juice through the cigarette lighter. It didn't actually jump start the car but fed just enough current to light up the dash and activate the trunk release. Everyone should own one of those, there must be many off brand versions now.
The B&D unit is discountinued but here's one I'm going to try from Amazon. I also keep a Cobra Jump pack (connects directly to battery) in the cubby, I used it a couple of weeks ago to jump start the car after the 5 year old battery kicked the bucket. It only had half a charge but the car fired right up. So this Wagan thing will go in the cubby too.
http://www.amazon.com/Wagan-EL9796-Quick-Jumper-Jumpstarter/dp/B00005OWK2/ref=sr_1_2?ie=UTF8&qid=1459879767&sr=8-2&keywords=cigarette+jump+start
by the way where is the positive terminal here:
