Edge used an infinite sustain guitar created by Michael Brook.
In terms ofrecreating it, a Fernandes Guitar Sustainer is one option, however I believe that option requires significant modifications to your guitar. A Sustaniac system looks a little easier to install & I've heard good things about it.
Easiest way I know of is to get hold of an E-Bow. They're are fairly cheap and from what I've heard they sound quite good.
Here's couple of links for info about the Fernandez system, Sustaniac & the E-Bow.