Display all paint slots simultaneously? Is there any way to show all layers (paint slots) at the same time in texture paint and solid mode like in most painting apps?

Currently the default behavior in 2.72 seems to be that only the selected layer is shown even though there are transparent parts on the layers.
I eventually found a way. It doesn't really feel like a proper solution but it works. In Cycles, you have to switch to material mode and you will then be able to see all layers. But the problem is that your object will interact with the lights so you have to also temporarily make your material shadeless.