I've done this before to a somewhat lesser degree and here's what I did.
1.Healing brush/clone/patch away all the hairs, sometimes it helps to do this on a layer sent to lighten first then again on a normal layer. I didn't really worry to much it it looked all messy and gross because after this you...
2. D&B the heck outta the parts you fixed because I honestly feel like there's no simple&good&fast way to get ridda those hairs you really have to spend a lotta time healing then D&B
3. (optional)Draw in some new hairs near the edges to help keep it looking real, do this with the clone tool and a very tiny brush with the opacity set down a bit.
Sometimes though if I'm in a rush I'll create a surface blur layer (I know, blur ahhh!) and set it to lighten or normal if perfection isn't a big deal with the part that need to be fixed masked. You still have to do the other two steps it just makes it go a little quicker.
All that being said, if all the hair is messy like that, sometimes having a nice smooth cut off looks weird, so make sure all the rest of your hair is nice and tamed after you do this!
Here's an example from my port: