I tried applying a little Toppik on my lace piece before. I disagree with the consensus here that it will stain the lace. This was not the case for me. It did, however, make cleanup a bit more difficult (although not by much), but as Hersute mentioned, it was worth it to get the look I was going for.

Just make sure you hit the Toppik with alcohol and a Q-tip and it should come right up.

EDIT: I should also mention I've only tried this on a small area, so unsure how cleanup will be on the entire hairline. Though I still don't think you'll have any major problems.