I would cross drill it and put a bolt and nut in there. If the fit is loose I might also use a shim or an epoxy such as JB Weld to help prevent it moving around. Such a repair should outlast the bicycle. Even if the repair were to fail, it would result in nothing more than a loose seat, gravity would hold it in place unless you are doing flips. I do not see that a repair using a cross bolt would present any kind of a safety hazard, and failure of the bolted repair would be highly unlikely.