Thanks OP! Already own it for the 360, I doubt I'll be playing this again anytime soon but you can't say no when it's free.
[quote name='Jackie Chandler']Mind sharing how you do that? I'd rather not have a one-time-use client floating around my computer if it isn't necessary.[/QUOTE]
Go to Gamefly.com, then in the search bar type in Bioshock, you should see it for several platforms. Pick the one that says "Free Download" in red, it should take you to a checkout page. Proceed through it, and done!