Just catching up on this thread. It's great. I'm not kegging yet but it certainly gives you something to think about.
I've got a mate who lives down the south coast (NSW). His recycleables wheely bin has a divider down the guts of it. Paper one side, glass and plastic the other.
If you could score one of these, (or add a wall to a normal bin), you could put ice in one side for your lager keg, and your ale keg in the other side so you serve the ale a few degrees higher. A multitemperature wheely keg.
Not sure if this would work - but say the ice in the lager side still cooled the ale side somewhat - you could put a small 12V PC fan in the back of wheely bin to pump outside air into the ale side of the bin to raise the temp to the desired level (???). Connect this up to a simple mechanical thermostat and run it with a small 12V battery that you stick inside the lid. Open the lid and you have the battery and thermostat mounted side by side.
If the assumption is wrong and the lager side doesn't cool the ale side through the "wall", wack the PC fan in the dividing wall and pump cold air from the lager side to the ale side as needed. or insulate the wall with a cheap sleeping mat and do it this way??
dreams of a non kegger..........