mfrasier Where there's a will there's a way. Is this what you're trying to achieve?
If so, then yes, it can be done, with some limitations. Depending on how you're using the mask this may or may not be a viable solution. For some use cases, its probably inappropriate, but there are multiple ways of getting the desired effect in which one is probably suitable. This one just happens to be quick and dirty.
Ive written a much more in-depth, optimized SoftMask solution for haxe-starling but I would be happy to port it to as3.