You could siphon but then you'd be needlessly exposing your brew to oxygen. Theveganbrewer's suggestion is the best path. You basically want to make a short jumper to connect two kegs together and transfer just the beer to a new keg. The trick here is that to avoid picking up the hops you want to hook up to the problem kegs liquid post with your CO2 and use the gas post to transfer the beer out.
The flow patt would be CO2 into the problem keg via liquid post, beer out the problem keg via gas post, beer into new (sterilized/purged) keg via liquid out post, CO2 out of new keg via relief valve
Since the gas post is so short you need to keep it on the bottom of the keg to draw liquid. Lay it on its side as suggested by TVB or upside down if you can support it somehow. Just make sure you give the hops time to settle once you position the keg. If you get impatient and leave them in suspension then they could get sucked up again and clog the transfer.