Scenario:
We have a slave node where different versions of a toolkit are installed in separate directories. Each version has a set of environment variables that need to be set during a build.
In a matrix project we want to build our software with each version of the toolkit.

Proposed solution:
On a node's configuration page one can group a set of env vars and give them a label. In a matrix project we use this label to build on this node with the grouped env vars.
It should be possible to create more than one group-label for one node.