Is there an easy way to do this?

For example assume I have a rectangular part already extruded. Then on that part I sketch 2 circles. I want to leave the circles where they are but cut the rest of the rectangular base by a given length (so the 2 circles would essentially be like legs supporting it).

I know I can go back and make my original part shorter than it needs to be and then draw the circles and extrude them to length effectively doing the same but asI already have a complex part it would be a pain to do this since I'd have to go back and check where all my dimensions are referenced to.