Try placing a piece of kitchen roll on top and then ironing over the top of that. The wax should re-melt and get picked up by the kitchen roll.
I don’t have any other ideas if you can’t get an extension lead to your car to use the iron, I’m afraid!
Get as much off as you can with wax remover, if it’s a big spill sticks help scrape it off and then try the iron trick over greaseproof paper (not if you have heated seats or it could melt relevant parts, same with the wax remover don’t just pour it on if you have them), then don’t sit on it without a plastic bag over it til you can get the seat cover replaced. As someone that is very very clumsy, I’ve got it out of carpet, clothes, a microwave lava volcano, walls, curtains, linens....it comes out really well but it some places it will always be tacky to touch and look off colour with a candlewaxy texture. if someone sits in that seat wearing something nice one day the outfit may not last the journey. I have a fave work out fit with one tiny wax blob that I love too much to part with. I’ve had it 5 years and it’s still sticky in that part but nowhere else I’ve had wax on. It’s just like gimme a break.
My last huge spill (and hopefully my last) Wax a lot of strip wax that had a piece of plastic broken and missing from the bottom. Saw the piece of plastic in the box after it happened as I was like...hoowwwww?? It fit perfectly. I’d unknowingly heated up a pot with no bottom and it went everywhere and I mean everywhere. It was flying out the doors! Funny looking back. But took approx 3-6hrs to clean up with a trip for an extra 5litres of remover and a thrown out brand new wedding gift £70 microwave.
I think for spill prevention it’s not worth heating wax before going to a client. Afterwards putting lids on the wax and the wax pot (not the heater the bit it comes in) after and tightening the actual wax with elastic bands, keeping in a separate boot box to everything else like a plastic tub with a lid that can be cleaned easily. But after any big spill we get really into this so you will find your own slick way good luck!