Gx20 plug is a nice and easy way to get a balance port happening with a nice screw on cap for weatherproofness
Or there is this guy;
Looks to be a lot more slender but probably a lot harder to work with due to it being so small.
I haven’t got one of these in any of my own builds yet, but if you can afford a good 12s balance charger (4-500 usd) it really seems like the best way to do it.