If you prefer sanding, lay in the minimum required structural fillet, then when it's just past "tacky", apply a thin layer of epoxy thicked with micro-spheres (glass bubbles) tinted with wood fiber. Pull up the masking tape. Do a light sanding to smooth out. I like the idea of coming back with IPA.

: Um, at the risk of sounding like a dumb neanderthal -- and no offense to the
: innovative solutions offered by others here -- I don't think fillets
: should be all that tough to deal with in the context of the overall
: project. What worked for me was simple: Mix wood flour with epoxy thick
: enough so that it won't run. Work NEAT. Sand off any excess. Presto!
: Perfect fillets.
: Since the fillets are thin anyway and generally exposed, they sand very, very
: easily (at least compared to the entire boat after it's glassed). Plus,
: with careful sanding you can mold them exactly like you want.
: I don't know. I've only built two boats. And sometimes on these bulletin
: boards, I find problems and solutions are more complex than necessary.
: It's understandable, though, because I know these projects and the idea of
: tackling hardened epoxy can be daunting. Good luck with whatever solution
: you come up with. As for me, I'm hoping the sanding strengthens my arms
: for the upcoming paddling season.
: Cheers, Grambo