Filters that are designed to be mounted in any position other than open end up will have anti-drainback valves. If they don't, it will be a problem. I would mount it anywhere, keeping the open side up, as has beeen stated. You can fill the filter before mounting it when you do oil changes when it is "right-side-up". I noted that you said "line drain back" in your post. The line voluum is inssufficient to worry about.
