I see I come here a bit late but if you are still listening ...

I have done this a couple of times, obtain suitable electrolytic capacitor(s).
I would suggest 500-1000microFarad/16v, solder 2 or more in parallel and then solder to the ESC +and - terminals. Electrolytics are polarised so observe the polarity. I would suggest heat shrink the terminals and glue with some flexible glue. The capacitor should be of a decent quality low ESR if you can get them, 105 deg C rated. The ESR and temperature rating is not critical but will make it more reliable.