Insulation, Radiant and Vapor Barriers - Floor over concrete basement slab -- got it backwards?

I was reflooring a corner closet in the basement, and I think I got it backwards.

I pulled the carpet and the pressed fiber mat underneath it, plus the tack strips, to reveal the slab. I checked the humidity by putting down plastic taped at the sides for 24 hours and got only the smallest amount of water, like less than the width across of a pencil eraser. After I patched the little holes in the slab where the brads in the tack strip had fought back, I put down 3/4" exterior grade plywood (removed the tension and curve by scoring it with a circular saw every ten inches or so) over a generous amount of adhesive and then tapcon-screwed it down with a hammer drill.

Unfortunately, what I didn't do, and should have done, was to install some sort of vapor barrier plastic underneath the plywood. I don't feel like redoing it (read: I'm not), but I'd like to have something down underneath the linoleum, just the same. Can you think of any spreadable products that would give me this vapor barrier ability and then allow me to place linoleum squares down on top?

The vapor barrier in my opinion is not needed anyway. It would only trap any moisture drawn by the wood. I would just be sure the plywood is clean and splinter free and lay the tiles. If you insist something be over the floor use a polyurethane sealer.

No VB on the floor! You did it right.