I set up a keymap that disables all keymaps, and then I can assign that keymap to a character. There's a button to disable it, and/or when I assign it to the next character, it automatically drops the keymap on the prior character.

If you're using the BoP trick there's no reason to kill Oghan. He doesn't hit very hard until the target has you know, at least 3+ sunders, and then you just drop stacks. Killing Oghan first isn't that bad. You'll take a lot of deaths, but if you stay focused and keep grinding/mitigate as many deaths as possible, he'll stop enraging eventually (1 minute) and then you can clean him up. Since you're alliance, there's no reason to risk this method, though.