Swapping hands
Yep - another lefty, though I spent a lot of time on shared computers so the mouse was generally on the right. When it was just my machine the mouse was on the left. I originally swapped the mouse buttons but eventually settled on leaving left button as the left button and giving it the middle digit instead.
It is a skill that has come in handy time and again when providing support or giving training and when doing a task that required considerable numeric keypad entry in combination with mouse use (not a great interface design!).