So long as there's a good amount (1/4"+) sticking out, find a good 12 pt socket that will slip over it, then hammer on the bleeder (most are very soft steel) till its expanded to roughly the widest ID of the socket, then bang the socket on making your very own 12 point bolt head. All the hammering helps break it free, plus you now have the best possible grip on the fastener. Good thing to try before breaking out the drill.
