The old "That assembly does not allow partially trusted callers." problem

Okay I have read every post in the world (or almost all of them) with regards to this wonderful message:
"SecurityException: That assembly does not allow partially trusted callers.]"
None of the posts address the main problem with this error message, which is "What do you do if you are in a hosted environment?"
> You Cannot Change the Trust Level
> You cannot put your assembly in their GAC
 
I Have:
Strongly signed the assembly
and used [assembly: AssemblyKeyFile(".filename.")]
employed [assembly ...