We don't have official support for gift purchases, but it's still possible.
If they don't have an account, the easiest thing to do is just to log out, then enter their email address when you check out. Then just email them and let them know what password you created for them.
If they do have an account, then enter a fake email address. Once your order is complete, let me know what the fake email address was and what your friend's email address is, and I'll move the order over for you.