I'm so happy I don't have that problem as I'm using the needle & thread (or knot) method and cut all the plugs before rehairing...
With the exception of forelocks, fringes, mohawks and such, but in those cases a straight cut is what I'm looking for.
With the tool I would try to cut the hair into a suitable length beforehand if possible, so that you'd only need to trim the uneven ends. However, if you absolutely want or need to cut it after rehairing, I guess what Maniah suggested is the way to go.
(And the point of this post was...? I don't know, lol. Hope you'll find a way to get it the way you like!)