In a corner, the rounded tip of a Sharpie marker worked well for me. I also have a 4" length of 3/8" o.d. Teflon pipe that's handy on straight corners. The technique I used was to mask off the area on either side of the bead, apply the flox, then remove the masking tape with the excess flox. One final pass with the tool feathered out the edges. Sometimes I would use peel-ply over the joint.