The point of the current procedure is that abcl-contrib.jar is not on the classpath at all, so it should be less configuration. That being said, I'm always open to easier ways for deployment as long as it doesn't break existing usages.
I'm "on the road" camping right now so I really won't be able to work on this until perhaps September.
A thought might be that the user can extend the CL:REQUIRE mechanism by pushing closures into a special variable whose name is something like *module-provider-hooks*, perhaps in a local system.lisp. This path may allow some experimentation before we merge those semantics with those of ABCL-CONTRIB.