Sorry, no such tool. Also, how far should be dilated into the void? You will just end up labelling non-brain tissue, no?

Really, skull stripping needs to be fixed here. Suggestion - do you have other images in addition to T1w of the same subject? Say, an additional PDw and T2w? If so, strip each separately with BET, align to T1w, reformat T2w and PDw masks, and combine all three by voting.

TR