Another workaround would be to insert the Roof such that it is too big, causing the apex of the hips/ridge point being further past the desired gable overhang.
Then go to Plan View, and 3D Slice it, deleting the extraneous portion of the hip roof.
But then we still have the problem of the Wall needing to be modified, to extend to the bottom of the gable roof. Which can be done in a similar way-- Assign a Height to the Wall that makes it extend well above the top of the roof line; then go to a side view and 3D Slice the Wall (probably will need to Explode them first) and delete the extraneous portions.
Another (major) downside is: Once we do an Explode or Boolean operation on a TurboCAD Architectural entity-- e.g.: "Wall", "Roof"-- it is no longer a TurboCAD Architectural entity with all the features they have.