This is a Goobay wireless AC switch:

I won't show the remote, too much trouble.
The idea is two of these things on top of each other.
The regular one would switch off the mains to the other one, in other words:
mains --> receiver --> standbykiller+transmitter --> appliance.
If the appliance should draw less than 5W, a circuit should activate that will activate the transmitter, that will cause the receiver below to switch off.
In other words I am trying to modify a defunct receiver/switch to become a standbykiller/transmitter with different components inside :p.
So I am reusing the housing of the unit you see above, so to speak

But my electrical skills are severely limited so I am trying to paint a picture of how this should be done.