This is a socket designed to hold a 5mm LED and battery without trimming the leads.

http://www.zheng3.com/2012/06/06/socket-to-me/

Feed the leads through the holes at the top of the socket. Insert the battery through the hole at the bottom of the socket. If the bulb doesn't light, flip the battery around. It should be a snug fit.

Once the bulb is lit, bend the LED leads around the bottom of the socket and press them into the side grooves to keep them out of the way.

This uses a DL1025 or equivalent battery. Amazon sells them for about two bucks: http://amzn.to/LkNAx8