...HOWEVER the later-model Nighthawk 750 has a sleeve on BOTH sides. There is not only a throttle sleeve on the right, but also one on the left by the choke cable.
This is wrong, someone must have added one to yours somewhere down the line. Mine only came with the one on the throttle side and I bought it new back in 2002.
My heated grips have sleeves on both sides but they are different diameters just like normal grips. Cant you just cut the sleeve off the choke side of the bars?

I still have my factory grips and will send them to you if you can use them.