Steve, I agree with the previous responses. The Rotozip would leave to wide of a kerf plus the possibility of slipping. I found this little keyhole pull saw at Orchard for about $8.00. I drilled four or five 1/16" holes for starters and connected those hole with a utility knife just to give the saw a groove to start in. It was real easy to control and went pretty fast. As you can see by the pic I didn't have any radiused corners but I think it would take the turn it you stayed perpendicular as you went around. Might be worth a try for $8.00.

Good Luck, John