Which Hassie lenses do you have? On my Contax 645, I use the 210 mm Sonnar with the 80 mm Planar reverse mounted on the front of it. The filters are the same size, so I just superglued two Lee filter holding rings together face-to-face to hold the Planar. It works well, but the setup is prone to vibration - solid tripod, mirror lock, no wind, etc, are all essential. You get a 210/80 = 2.6 magnification ratio though.
The other setup I use with the Contax is 1.4 TC + 52 mm extension tube + 120 mm Macro Planar fully extended. That give just over 2 magnification.
I haven't tried reverse mounting the 80 mm Planar on front of the second setup ... now there's a thought.