Sounds like you already understand this is temporary, but heres the method I have used in the past.
Scrub the tiles clean, dry and then clean again with TSP(being careful around glass because it etches glass), then degloss tiles with a very fine aluminum oxide paper, then use xim primer(probably the best primer there is), then apply either a high gloss(quality paint) or epoxy paint if theres high humidity. Sounds like it may be easier to just retile.