In reply to Sutty22:
Its not commonly done at all, and would be very dodgy unless you get it absolutely right. More common would be to get hold of another rope so you could utilise the belay stakes, bringing a crab to the edge of the cliff for you to hang your main rope. Thats what the stakes are there for, and would be a lot stronger than 3 nuts in the rock.
The easier option is that the belayer anchor himself to the top of the crag, throws a rope down and belays the climber UP the climb from above. Far safer.