Thanks for the quick reply. I’m getting closer, but don’t have it working yet.
I have found that control-macbookbutton does something, but what it does is different than what I get from clicking the right button of an external mouse. But it is what I get from control-right clicking with the external mouse. Maybe Vine VNC is intercepting the control to turn it into a right click, but the control is still being passed through to the server so that the window manager picks it up as a control-right click (yeah yeah – crazy old school Linux window managers with a gadzillion buttons and option-button effects). I haven’t found an option to tell the mwm window manager to treat control-right click as the same as right click.
I experimented with using xmodmap on the Linux side to rebind the pointer buttons. This seemed to affect only the external mouse buttons, but not the macbook button.