Yeah, I suppose you can (haven't tried it yet). Just wait for fermentation to settle down and krausen to fall; I expect the CO2 would scrub off all of the aroma, negating the effects of dry hopping.
I tend to dry hop in the keg.Hops go into sterilized hop sack and are left in the keg for 4-5 days and then removed(before carbonation levels get to high).
If dry hops are placed in at the start of fermentation then a guess you will lose all or most of the hop aroma!!!
Yeah just dont forget a mesh hop sack! I thought I could get away without one, ended up with little bits of hop floating in my beer. I made a crafty filter to put over the keg tap, though, which ended up giving the beer a better head too