Yes it is possible, but I had no luck whatsoever with pressing the new bearing into the pulley. The main dealer quoted £140 for a new pulley/bearing (fitted) so I may go back and ask them how much they want to just supply the pulley as it's a really simple DIY fit.
Here is how to remove the pulley:
Loosen drive belt tensioner
Remove three nuts securing metal shield to top of compressor and remove shield
Undo and remove the bolt in the centre of the pulley, then gently pull the round plate out. Be very careful as there is a washer (possibly more than one, mine only had one) inside the barrel that fits into the compressor, do not lose them.
You will now be able to see the pulley and bearing. Remove the circlip, and you should be able to gently persuade the pulley to come off. Don't hit it with a big hammer or use anything too extreme - mine came off with plenty of Plusgas and some gentle levering with a screwdriver between compressor body and pulley. At this point you can obtain a new bearing for £40 or so, but as I said I tried to replace it and only succeeded in damaging the new bearing seal and contaminating the ballraces, so it made an equally annoying whining noise on reassembly.
Unless you have a proper engineering workshop at your disposal I would be more inclined to ask how much the main dealer wants for the part - the £140 quote probably included an hour's labour so it should be cheaper to just buy the component.
