Gluing rigid insulation – GreenBuildingAdvisor

I’m looking to put some rigid foam board insulation in a standard 16″ stud cavity. Not for an entire house, just in one stud cavity to prevent a conduit that’s running against the back wall sheathing from getting cold.

The stud cavity is framed with 2×6 studs. I think the best best would be 4″ of polyiso rigid foam. Can I glue two 2″ boards together? Finding 4″ isn’t proving easy. If so, what glue would you use?

Also, would I cut the foam board slightly smaller than the stud cavity and foam the edges?