If you switch to cat, the power bar becomes the energy bar. Which updates as fast as necessary, if you have frequent updates for power enabled. I don't understand what you are trying to do? Why would one need a second power bar?
Especially if it is NOT to display druid mana in cat/bear?! Which, btw, could be done with a tag, easily, no need for a bar.
![Roll Eyes (Sarcastic)](//cdn-wow.mmoui.com/images/style_mmoi_wowi2/smilies/rolleyes.gif)