From what I read, the rumble pad and the Dual action are the same thing .cfg wise. But since I don't have either, I can't test them.
You just might have to wait till 4.1.
Or if SSL allows the use of the 4.1 Rumblepad now, we might be able to hack one together. But if you google just "Logitech Dual Action .cfg for source" there are some HL2 tuts. to get them working, should be similar for GE:S.
If you can get that far, we might be able to tweak your .cfg and get it working.
But since this game is made for KB/MS, there really isn't much support.