Please feel free to add your vote to the “Add a configurable hotkey for Route Differential Pair tool” wish in the bugtracker.
Again, it’s already there. 
When in track mode (press ‘X’) press ‘6’, now you are in differential pair mode.
Also, ‘7’, ‘8’, and ‘9’ will select the other items in the Route menu.
Well, hotkey “6” and the rest are hardcoded and I mean adding a “configurable” hotkey 
I’ll change bug title to reflect that.