I have a local package repository that contains software that I want to install in a different install_tree than the normal spack location ($spack/opt/spack). Is there a configuration option that allows me to do this?

The idea is to keep installations of proprietary, locally developed packages separate from open source packages provided by spack. As a work around, I may be able to hack ~/.spack/config.yaml to temporarily use a different install_tree, but this is cumbersome.

Any ideas on how to achieve this layout?