Here's the final iteration of my 12mm box end conversion
I ended up using one of those socket adapter bits of which I have quite a few, luckily I happened to have a black one.
I was going to cut it off flush, but I realized that if I leave it sticking out i can put some kind of spinner handle on it.
I just happened to have this little nut driver laying around and it works perfectly, I think it may be from an Xcelite Torque amplifier set.
I've used this a few times in the past couplevdays and it works very well, the little spinner handle comes in very handy.
A big thanks to J.A.F.E and Strik for giving me the idea to use a bit driver adapter, works better than my first thing and was much easier.