Nope, not with the G-provider interface that's exposed to the public. Only right click on project items, or adding new icons that you can left click on.
Certified LabVIEW Architect
I should have looked better through the existing threads, it is possible:
One small drawback: I fail on creating buttons and pulldown-menus within one project provider.
Wow, not only was I wrong about this question, but I was wrong about it twice. Sorry to have led you astray, but it's been a long time since I dove into this framework.