IB2's hiding/fading code must coincide with a state/page change. So first set up your bar to switch pages on combat. Set up the contents in and out of combat using state emulation. Then set up your fade values for your states. Obviously, if you want your bar to do nothing when out of combat, you just leave the buttons empty when out of combat and set the combat actions up using emulation (because you can't make changes to button contents when actually in combat).
If you want me to, I can post an export of a bar that does this for you. (IB2 has Import and Export features. :) )
No you don't have to post an export, I did as you said and made 2 pages, i kept the actions in the non combat state too because i want to start the combat with one of them (using the keybindings) Works perfectly. :)
I just might considering a sex-change, just for you ;D...