Ask for help, activating same game twice on GFWL account

I have Batman Arkham City on GFWL account and want to play Harley Quinn Revenge DLC. But in GFWL store it costs 400 rub (the same price I bought main game) and I think its too much for DLC. Now B:AC GOTY on sale at steam store and I thinking to buy it, and steam version needs GFWL account too. So I dont know will can I activate this steam copy in my GFWL account and get the Harley Quinn dlc or I must create another account for this. Anybody have same situation?

And one more question. But I think the answer is no, anyway... Is it possible to buy at steam store only HQR DLC, get its key and redeem it on GFWL account?