Rush provides a setenv command in its rush.conf file that enables to set an environment variable value before rendering.

For more details, see the Rush documentation: setenv command

For example if you did not instal the Golaem Crowd package locally on each render nodes, you need to specify the Maya Module Path in this file.

os=windows setenv MAYA_MODULE_PATH "C:\Golaem\GolaemCrowd-3.0.14-Maya2012"

Do not forget to run rush-push after changing the file, so that the configuration files are updated on all nodes.

See documentation here: rush -push command