Dependencies: excluding a constant from reloading

The Rails dependency mechanism tracks which constants are defined when
anything is loaded automatically. In the development environment, these
constants are undefined after each request, so that possibly changed
versions can be reloaded for the next request.

Usually, that's nice and everything, but my current case it leads to
problems. I'm dynamically defining cache sweeper classes from within
a "macro" in my controllers. These cache sweeper classes are bound to
constants and as such are unloaded after the request. However, cache
sweepers are also registered as observers on the relevant models and
these registrations are retained across requests. Here's where the
trouble starts: observers are instantiated before the controller for
the current request is loaded. As a result, on the second request, the
Rails dispatcher tries to instantiate observers, the sweepers, that
have been undefined at the end of the previous request, but not yet
been re-defined on the current request.

Summing up, I need a clean way of telling the dependency mechanism not
to unload my sweepers. From looking at the relevant code, I can
probably wedge it in there with brute force, but that's not what I'd
like to do. Maybe I've just overlooked some elegant way to achieve what
I want.