My SRX has grooves all over the place and I was thinking the same thing. I saw some inserts to pretty up the hole in an aftermarket snowmobile catalog, but don't remember which one it was. I thought it might have been SpankysParts.com but couldn't find it again.
I just looked there and found they have one for a Ski-Doo Rev machine, but not a Yamaha. Called a Start Pull Trim Ring.