How can i start a logout script on Edubuntu with LTSP running

[X-Dimension]

Hello,

we are using Edubuntu 12.04 with LTSP in our schools.
I want to start a shell skript when a user logs out.
Lightdm  has an option called "session-cleanup-skript=", but in a LTSP 
setup LDM is used instead on
the clients.
How can i set a logout skript here?

Thanks for help.