Hi Joe,
I've built a lot of Bottlehead kits and have always just left the top plate free. I've even provisioned a few kits for top plate attachments and ended up not using them.
I just invert the top if I need to access the components. I think a lot of other users follow the same approach. Adjustments aren't typically so frequent as to necessitate something more 'real time.'
That being said, if one were to hinge the top, I'd suggest using simple hinges and some sort of prop rod or other temporary support.
David