tbsm may run desktop sessions, such as dwm, without consolekit and dbus
support.  Thus, given that tbsm detects available .desktop files from
/usr/share/xsessions, create a copy of the .desktop file and modify
the Name and Exec lines as such:
Name=dwm-dbus
Exec=ck-launch-session dbus-launch --sh-syntax --exit-with-session dwm