Stacks with transparent background

[David Bovill]

Before I dive in with masks, multiple stacks and the like - any advice on
how to achieve a stack with opaque controls and a transparent background. It
seems that due to the nature of the inheritance using the blendlevel to make
the stack window transparent means that all of its controls will be at least
as transparent - so you cant have an opaque control and a transparent card
background / window.

Maybe there is a nice trick here with inks? The only thing I can think of is
scripting something to create a mask or use multiple stacks.