A not always, but usually sucessful method is to use a hypodermic and inject vinyl adhesive through the bubble. Tilt the needle around in the bubble as you inject to help spread the glue, then remove the syringe and work the bubble with a rolling motion. Follow by working from the outside of the bubble towards the center to squeeze out excess adhesive. Allow this to set for a day or two, then seal over the hypodermic puncture with a drop of clear nail polish.
NOTE: This does require a fairly good sized hypo needle, and sometimes you may also need to slightly thin the adhesive to get it to flow.