FCP 7 / How to affect just a portion of the frame?

Lets say you are shooting from inside a car and exposed for the interior but that leaves the view out the window blown out.
IN FCP is there a way to designate only a certain portion of the frame to adjust the brightness and leave the other part of the frame alone? Without creating another layer and a mask. Just on the original layer? I know that in Premiere there a few plugins which you can create a vignette, and then reverse the vignette and adjust only the part you have designated. Anything like this for FCP7?
Thanks Guys!

If it's just a frame, take it to p.s. or better yet, Aperture.
DD

Take the clip you're working on, duplicate it and put it above the original clip. CROP the duplicated clip so that only the top of the screen shows. Apply filters and it will only happen to the top of the screen. To better blend the effect, be sure to feather the crop.

Or better, better, do what Joe said.
DD