I'm not aware of anyone doing it, but, IMO, heat shrinking the tubes into the stubs makes the most sense. I should be quite possible to machine a diametral step into the stub (smaller diameter forward) and matching one on the tube. Thermal expansion is relatively easy to control and the stubs raised to boiling water temperature while the tubes are "frozen" in ice water would make a 180 oF difference. If trade workmen can control diameters to allow known force fits, they can surely also do it for a shrink fit. I've never done it, so this is an IMO.

DDA