Is something like this reasonably possible?
Not in Mach3. You're looking for tabs, which are done in a CAM program that creates your g-code. Vectric's Cut2D lets you easily add them manually.
http://www.vectric.com/WebSite/Vectric/cut2D/c2d_features.htmIf you step up to V-Carve Pro, it'll add them automatically.