I've been playing with a borrowed N900 with a view to obtaining one for myself, and this is the first issue I have been unable to solve on my own.

Basically, my current phone is a N95, and I have it configured to always go into PC Suite mode as I never use mass storage mode, but I'm unable to find a similar option on the N900. I've had a look into "PC-Connectivity Manager", but I can't seem to get it to do anything (I've set "PC Suite" mode in the default environment, but the N900 still prompts me when I plug the cable in).

It's not possible from what I know.
It's closed source btw.