Oh thats not a bad idea. Is that a specific type of solder or will any work?
Lemme just go raid fort Knox and grab some gold real quick..
Mount the end cap in some kind of solid holder (a large vice is a good choice) and heat it up with a propane or similar torch. Melt the solder into the cap so that you have a "pool" of solder to dip into.
Clean your copper rings, perhaps dip/wipe in flux - then dip the rings in the solder (you might have to fashion some kind of tool to allow for this, of course).