Pretty much the technique we use on our app in the "drop-in"/"add-in" modules. Since there is no reason to include duplicate the main procedure library in the "drop-in" module, we just use a "stub" version of the procedure library files (i.e. only the function and procedure headings) that's added to the project files and set them to excluded. Similarly, in the section of the main application that uses the "drop-in" module, we add a "stub" version of the procedure library representing the functions/procedures in the "drop-in" module and set it to be excluded.