the glob feature can do this for you, there is no gui interface for it yet, so you need to adjust your cbp file in an editor.
Remember to reload the project the moment you added/removed files in that directory
Example :
<UnitsGlob directory="../export/" recursive="1" wildcard="" />
<UnitsGlob directory="../local/" recursive="1" wildcard="" />
You put this at the spot where normally the <Units> would exist. wildcard empty means the rules that cb use (just like when you add files via the gui interface), but you can specify your own wildcard pattern.