i have done the method that johnny speaks of.
you have to be VERY careful that you dont loose the valve into the cylinder, that makes baby jesus cry.
either using the compressed air OR rotate the engine till the piston is on TDC will work.
dont loose any of the collets or retainers, they are small and are easily lost, specially in the head and down the oil return, again, baby jesus will be crying at that.
doing the job with the head of is a bit easier but takes more time (with the head removal and all). doing it in car is quicker but not recommended if your not confident from the start.
