I really hate to rub salt in the wound, but......
You also could have just hit "alt + L" (a default key bind when Carbonite is installed) to bring up the Blizzard quest log and used the item there.
When you deleted Carbonite through your Curse Client, there's a very good chance that you also deleted all of Carbonites saved variables, which means you're going to have to set it up all over again on all of your characters (if you have more than one).
Another alternative for using a quest related object would be the way I do it: I use
Dominos for my action bars, and I keep one slot clear that I always use for quest related items. I also have that slot key bound to "shift S". Since I keep my Carbonite Quest Watch window (quest tracker) minimized unless I really need to look at something in it, it's a bit difficult to use those items from there. I don't know if that would work with the default action bars, but it
should work with any action bar replacement addon.