If using compression, remove the non-compressed map file, leave only the <map name>.bz2 file.
In theory, you'd need to remove /addons/<add on name> from every file you wanted to force that isn't included automatically.
Example. /models/weapons/<3 model files> (I think, not sure about the first slash in front of models, or if all 3 files need to be in the list..I think I remember seeing somewhere, perhaps in the wiki, that if you included just one file extension, it would download the other two or three files associated with a model..or, maybe I'm getting confused with)
I say in theory because, 1) I've seen people say they use whole path and 'it just work', but, I'd try first and it's worked for me in past, 2) addon folders are virtual... /addon/<addon_name>/models, in effect, to Gmod, becomes /models/<model files>
It's the same with lua/textures/models/maps in addons folders.
Hope that helps.