Yes, I have had success softening oil based paints with ammonia as well.
Also, as a last resort, I have soaked a brush in paint stripper - the bristles become rather soft, but the paint is gone!
An inexpensive and effective way to rescue a brush is to soak it in ammonia. Suspend the brush (as suggested previously) in a container with household ammonia, and let it soak for a few days. The ammonia will disolve dried paint and the bristles will become soft again.
The suggestion to use...