It is always the best practise to include "global.php" in a vb integration project as it will allow you use all vb class&functions/template system in your code as well as vb will be handling all of your concerns like user/session authentication etc. So I don't see the point of avoding such an inclusion considering the fact that you are after a vb integrated solution.
Meh, I guess you're right really. For the moment I'll try including the vB3 global file and perhaps come up with something more elaborate at a later date.