MB,
I've looked at FiveMega's pics but its impossible to tell how large the opening is under the bi-pin socket. What I envision is machining an alum. heatsink / drop-in that would press into the opening allowing a mounted LED and using a M@G sized reflector from a parts supplier. The matching tailcaps have been sold-out for some time so I'd settle for a SF S6.
I suppose for a multi-emitter light using a Sandwich Shoppe universal M@G sink might work pretty easily if you could fashion a bi-pin plug to fit into the socket.