I go back and forth a bit about this. More often than not I do as Major suggests and just dry hop in the fermenter until the pellets drop, around 7 days. In fact, after reading this thread I just went and dry-hopped 2 IPAs in fermenter buckets currently 1 week into the ferment, that I had planned to keg hop.
So true that keg hopping is a bit of a PITA.
I still think there is a hop fresh flavor dimension only achievable when keg hopping, and I wonder if some dry hop flavor is lost in the fermenter due to the hops getting immersed in the yeast cake. And of course not a good idea to re-use that yeast. My keg hop process is to add the dry hops in a small -medium size, small mesh nylon bag with nylon drawstring tightly closed and knotted, and hang the bag to a keg lid tab with hole in it welded onto the underside of the keg lid. This keeps the hop bag and string entirely inside the corny keg. I dry hop in the keg the first 3-4 days at room temp, then another 4 days at kegerator temps, and then remove the hop bag, squeezing it some before removing.