I didn't research this yet, but e.g. the OMweather applet does this, so I would assume this is already supported.
Managing launcher-applets by application will quickly clutter the applet selection GUI (which on OS2007 doesn't even scroll correctly with too many different applets/plug-ins installed) - adding them per application, when all the necessary information is already there in the menu *.desktop files also seems not aesthetic. Take a look at simplelauncher! The only things missing are multiple rows (there was another launcher I tested that supported this, but was overengineered in some other aspects - don't remember the name) and going full screen with the desktop/home area/"backdrop" (newtonese).