Even .5 - 1psi cracking pressure should do it. Even if it doesn't completely, it will, at some point, manage to contain most of the mass. Much depends on how the lines dip and up turn as well as the filter's elevation above the "drain plane" (either forward or backward). Eventually you should get a vacuum'd column of oil with a slight air gap that can't travel past the upturn in the dipped line.
You can go the check valve method, but if you've got enough flexibility to run the lines a bit below the sump, you may be able to avoid spending the money. Air will travel laterally, it will just compress itself to one very long shallow bubble, but it can't travel down into a liquid where the liquid has to be lifted against gravity ..and the bubble must pass through it.
I don't know if I'm describing this well.