Partially collapsable bars? How would I do this? Can I?

[hidakiya]

I saw someone with a Flexbar setup oh-so-long ago where, for Shaman totems, there would be one visible box with the last chosen totem, but with a right click, the rest of the buttons above would show. A right click onto one of those buttons would swap the totem to the active button and all that jazz.

Is there a simple way for me to do this? Is it even possible? I'm not sure if I'm wording this correctly, but some assistance would be lovely.