Workspace Assemblies Extensibility Rule

Has anyone been able to get an extensibility rule to work in the workspace assemblies? I've looked and I haven't seen much of any documentation on this. I'm working in 8.4 and have the rule working when I have it using the regular extensibility business rule which is attached to a DM job to run. When I try to move it to a workspace assembly and put it on a DM job it doesn't work. I've created a new file as the Extensibility Business rule source code and have the same code with no errors. I don't see an option in the Ws Assembly Factory to specifically call out extensibility rules either. So far I've been successful with getting an XFBR, Extender Rule and Custom calculate rule to work in assemblies but extensibility doesn't seem to work. Below is the error I am getting.