force specific shell environment variable on process using /etc/pam.d/ rules

I am using slim login manager, and it has its own pam rules file: /etc/pam.d/slim. auth requisite pam_nologin.so auth required pam_env.so readenv=1 auth required pam_env.so readenv=1 envfile=/etc/default/locale @include common-auth @include common-account session required pam_limits.so session required pam_loginuid.so @include common-session @include common-password it seems that the pam_env.so rules are setting the environment variables for the running process, such as: USER, HOME, PWD, SHELL, ... Is it possible, after these have been set, to force SHELL to be /bin/sh? I mean, regardless what shell user has specified in /etc/passwd, I want to force to use /bin/sh for slim process.