I'm just throwing this out there - I'm sure there's plenty of reasons it wouldn't work...
Say you get 4 of these, or similar (the pic is from the website Arizoni suggested):
http://www.aircraftspruce.com/catalog/appages/ms21919clamps2.phpI used a couple like these to mount my rack. Thread here, with some pics:
http://www.enfieldmotorcycles.com/forum/index.php/topic,15273.msg166010.html#msg166010Install one on the curved fender support rail right up near the shock mount - could even be inboard of the turn signal. "Fabricate a bracket" (don't you love these detailed suggestions?) that can have a hole drilled to bolt to the clamp. The bracket angles down and back, below the signal, then turns and runs straight and level, back until it meets the rail again, near the tail light. Attach it using another clamp.
Cheesy pic example: black clamps, green bolts, and pink bracket:
You'd have to sort out how long the level part would need to be to support your bags, and fine-tune the mounting points. Maybe the bags would be too low this way? Dunno, just thinking out loud.
Come to think of it, I might do something similar to install my crummy throw-over bags so I don't have to throw them over...