Hi,
as you might know an arduino-sketch (pde-file) has to be preprocessed by the IDE to turn it into plain C-code that is handed over to the compiler.
This involves searching for all library-include statements in the main pde-file, and adding a compiler-directive to have them included in the resulting upload-code.
But the arduino-preprocessor does not do this for your extra *.h or .*cpp in your sketch. So what you are trying is not possible (with the current arduino-IDE version).
Eberhard