I did exactly as you're suggesting.... but didn't do the exacto part. I used permatex liquid rubber stuff in a tube.. don't know if that's just rtv. Anyway... I made a big mess. Never thought about trimming 1st to get a smooth edge... duh.... as I was trying to get a smooth line on chipped trim. Please let us know how it works out if you decide to do it... and how easy/hard the exacto cutting was... Bill