I think this can definitely be done, but what I am afraid of is that it would look a bit silly. You would basically have same two parameters on screen twice for no reason. Aside from vertical sun angle being inverted in 3ds Max transform boxes, you would basically have two same values on two places at the same time. So if you decided to rotate sun 45 degrees right and have your cursor in a middle of the screen, only difference is you have to move that cursor pointer down, not to the right.
I still don't get what's so hard about it. Any other lights, be it regular max lights or corona lights, are transformed by native 3ds Max rotate tool, as well as is pretty much anything else in the 3ds Max viewport. So it should be completely natural to adjust sun angle using the same tool you adjust every single 3ds Max object with. It's not slower nor more complicated.