Supondo que você esteja usando o KDE4, você pode tentar uma chamada de linha de comando similar à usada aqui
De JanGerrit
Select allqdbus org.kde.powerdevil /modules/powerdevil setProfile <Profilename>
Replace with the name of a preconfigured profile you added (I think there's something like this called "Presentation" or something similar)
E ou
De Gen2ly
Came across today that dbus has an inhibit command i can use. Not the same thing but looks like powerdevil doesn't have the ability to disable power management.
qdbus org.freedesktop.PowerManagement /org/freedesktop/PowerManagement \
org.freedesktop.PowerManagement.Inhibit.Inhibit