Join Date: Jan 2010
Location: Golden, BC, Canada
Maybe a visual would help...
1. Mitred corners - no profile to the return
2. Bevelled Return - Profiled return, but the sawcut is visible
3. Combination - Return is profiled, Cut nearly invisible, but more work.
Clearly, the OP wants the 3rd look, and if I needed to do this, I'd make the initial cuts using a stop block on a mitre saw, then finish with a hand saw. (likely a pull saw) There likely would not be a router bit capable of getting a good inside corner, so that method isn't being considered.
Good luck on your project.
The Pessimist sees difficulty in every opportunity while the Optimist sees opportunity in every difficulty...