I have a 64 oz growler that came from Davidson Brothers brewery in St. George NY (good IPA!) that has a screw down cap w/ an inner plastic liner that is labeled "Poly Seal 5". The inner liner is raised in the center, and is designed so that screwing it down to the glass will deform the plastic against the inside rim of bottle neck, and seal that way.
It's designed for filling under a tap and bringing home. I'm not certain that it'll take pressure from bottle conditioning and hold it for a month or two. Certainly it never leaked, and I shlepped the beer back on a train from St. George to Manhattan, no problems.
Any thoughts? Thanks.