If you've got a 2009+ GS.
Pop along to your dealer and order (do a search on ADVrider or that OEM parts site for further details):
a relay
a wiring loom (it'll come with 2 fuses, tie wraps etc and instructions)
LED aux lights (you'll need to order two new style connectors)
light mounts.
aux light switch.
You can fit them yourself in a long evening, you don't even have to remove the fuel tank. You can just move it back (unplug all the gubbins from the FPC and hoses, which are all easy enough).
Unclip the ZFE unit, flip it up, shift the Bosch unit out the way, pop in the relay.
Put back the Bosch and ZFE.
Remove the blanking plate from the power connector in the ZFE lid, connect in the loom (can't recall where the aux switch connects to).
Cut off the old H11 style connectors, and wire in the connectors for the LEDs.
Connect everything up and test it works.
Now remove the lights, power off, make the wiring all nice and tidy (if you're unsure, take a look at a GSA in a showroom).
Screw in the LEDs to the mounts, screw them to the bike, done.
Then get a Les Wassell, HiD for the dipped light, use his ballast holder which connects to the oil cooler mounting (notice BMW changed the oil cooler mounting so you can't try and undo the wrong bit! in the 2012s at least). Leave the High Beam as the H7.
Set the beam to be a bit higher than factory supplied.
Now you can ride through anywhere you like in the pitchy black and don't need to pay dealer anything other than for the parts.