(I was only using __PACKAGE__ to see why things weren't being put in the right namespace.)

The sub Mod::foo { } suggestion was a new thought, but like __PACKAGE__, the magic identifier SUPER was not correct. I would rather use SUPER than hardwire the base class, but it's pretty arbitrary.

As for the many suggestions to rethink the design; yes, it's a good idea to rethink it. However, I've rethought, and in my particular case, it rightfully should be one class with a few semi-distinct duties that are not easy to aggregate or embed or delegate. I'm working near the base of a large class hierarchy, and the base classes really must cover their core duties.