[iTunes] Arrgh!

[henri]

It took me a few weeks to seperate my iTunes collection into 3 
different libraries on a large external drive.
Now I discover I can only load my iPod from one library at a time. 
Trying to load some from here and some from there causes a warning, 
iPod can only be synched to one at a time, I'd need to erase what's 
there before it will synch with another library. Any known way around 
this limitation? Managing manually of course.