I want to create a quick 'groove' in a trimmed surface. Something which is pretty common in ID work and simple to do in Poly modelers. I thought the right approach is Offset Inset with Groove, but alas all my tries have failed. Any help on how best to do this would be greatly appreciated!

Here's the file:
https://altuit.cloud/web/dbpub/3D/groove.3dm

Here's a video describing the issue:

http://www.youtube.com/watch?v=SHtipk_rML4