trimming feathered objects

[highfrontier]

I like using feathering for quick highlights and shadows, but I can't find a way to trim away to achieve the illusion of a sharp edge (see pic).
Clivview and using subtract shape works, but then applies feather to the result or produces a bizarre effect - annoyingly grouping makes no difference as the same thing happens when the feathered object is within a group.
Feather seems to be treated by the program as a top level effect that can't be modified.

Anyone worked out a way to achieve this or a nice workaround? I'm tempted to bring the drawings into photoshop and paint on the highlights and shadows, but this will slow things down.