I've been trying but it seems the blur does not follow custom shapes (i.e. lasso select). I've attached a picture (sorry for the crudeness) of what I'm trying to do: the red indicates where I have the lasso select tool selected; the blue represents the area to be blurred and then unblur in the space between the red and blue, fully unblurring when it reaches the red. Effectively you would have a "U" shaped gradient blur. The option to blur from the edge seems to make an estimated boundary overlapping the whole area instead of using the actual selected area.
Just hoping this was what I was loo