[boost] [extension] Concatenating factory_map objects

Hi, I'm developing a plugin system and I will be loading several DLLs. Basically, as far as I know, this means having one factory_map per DLL (on Windows). I need to concatenate either the factory_map objects or their maps so that I can do lookups in one map instead of several maps. Is there a recommended way of doing this? Right now this requires keeping all of the factory_map objects around (for cleanup purposes only) and having my additional global std::map, that contains the concatenated std::map's from the factory_map objects (it's essentially one large copy).