In reply to UniClimber:
You'd be better off just using it for front levering, so long as there's enough leg room, you might need to kick the desk back off, and pull your desk away from the wall a bit.
Alternatively, cut a big square or oblong hole in the carpet under the chair, keep the cut out, turn off the mains water supply, get yourself down HSS, Speedy, or A-Plant, rent a pneumatic drill, do a test hole first where your chair is, to check which floor you are on, if it's the ground floor, ideal, carry on, knock out a trench big enough to stand up in and just reach the desk top, line your trench with planks, use hard as nails to make them stick, get some thin strips to put on these as foot rungs maybe to assist hangs, use hard as nails again to stick them on too. Make a trapdoor lid for the hole, perhaps hinged, stick the carpet back on, use a staple gun.
Find a way to mount your fingerboard on the desk edge, so that you can easily remove it again when yr lunch break is over, and put it back in the desk drawer.
If you found out your not on the ground floor, tidy the hole up, make it like a trap door or attic, refit any lighting you knocked off back on to the ceiling below next to the hole, tidy the mess off the desk below that it all landed on, brushing any dust out of peoples hair too, explain to them that you'll just be dipping your legs down through the ceiling a few times a wk, buy them a massive Toblerone or tin of quality street.
Oh, if hanging into the room below, use a heavy duty theraband to help you get back up, or rope with knots, or see if they'll let you leave a step ladder in place under the hole.
Post edited at 11:15