How can I append a path to my PATH with home-manager for new shells using home.sessionPath without needing reboot?

Help
1 
home = {
  sessionPath = [
    "/home/b0ef/.foo/bar"
  ];
};

This seems to work when restarting, but not when launching new shells.

I see that it ends up in .profile

$cat .profile
. "/home/b0ef/.nix-profile/etc/profile.d/hm-session-vars.sh"

…and that contains

$ cat .nix-profile/etc/profile.d/hm-session-vars.sh
# Only source this once.
if [ -n "$__HM_SESS_VARS_SOURCED" ]; then return; fi
export __HM_SESS_VARS_SOURCED=1

export PATH="$PATH${PATH:+:}/home/b0ef/.foo/bar"
[b0ef@ximian:~]$

, but I want it to append my PATH for new shells, not needing to reboot.