For this, you will need to build it into the model.
In such cases, I usually build the model, copy it, and make the changes on the copy. This can be done several ways, but the easiest is just make a copy. If you may need to modify the model and want the changes to propagate automatically, make a new model using the DERIVE tool.
For this, I would probably sketch a profile of the tool and collet nut in a plane perpendicular to the contour (say the XZ plane) and sweep it around the contour I want to cut.
I have a few minutes, so I’ll see if I can dummy up an example.
edit: rectangular block. I filletted the corners with a 0.001mm fillet so there would be a smooth sweep path. Then made a work plane, sketched the rectangle, and used sweep to run it around. I set it as a cut to make the operation visible, but it should be done in practice as a join. Then use 2d adaptive to clear down the wide part to make clearance for the tooling. Whatever is needed to go to the bottom. Adapt the profile to whatever form needed, such as a tee shape for two side clearance.