I am sure others have come up with this mod before me:
However I could not find a modified keyboard ROM that does it, so I ended up making one myself.
This ZIP contains both the original and the modified ROM: 
InvertedT Apple IIe Keyboard ROM-341-0150-A-US-UK.zip
To implement:
1. Burn the modified ROM and swap it with the KEYBOARD ROM chip on the Apple IIe motherboard.
2. Pull and swap the three keycaps as shown on the picture.