1) Take up 'the position', learn to cope with the ache in your back.
2 ) Find brake light switch, unplug wires and then rotate it through 90 deg. Slide it out of it's 'keyhole' mounting (downwards)
3 ) Grasp the plunger on the switch firmly and pull (hard) until you hear a loud crack. Plunger will extend by up to 10mm and reveal a notch in the plunger.
4 ) Hold the brake pedal depressed
5 ) Re-insert (extended) brake switch and rotate through 90 deg to secure.
6 ) Now release the brake pedal
, it'll settle on the switch plunger setting it to the correct position.
7 ) Plug the (2) wires back into the switch.
8 ) Exit the footwell, massage acheing back!
Once done the brake pedal will be at the same height as before (the pedal adjusts the switch, not the other way round), but the sensitivity in the brake lights will have been corrected. It is a fairly commonplace problem and if left unchecked can result in brake lights being permanently on. Fortunatly the cure (in the short term at least) is free and easily done DIY. You can replace the brake light switch with a later model (may need to modify the mounting plate, not sure on this) which is supposed to be a 100% cure for it, but this means buying a new switch when the old one is still prefectly OK, just in need of resetting.
I suppose it depends on how often you have the problem. In my case it's happened to me once in 104,000 miles, but i have 'fixed' three or four of them now on others' Fs.