Taking one's hand off of a two handed weapon (or putting it back on) is a free action.
Some people house-rule it to be a non-action that you can do even when it is not your turn. I am not one of those people. Much like having your eyes closed or open, you decide at the end of your turn what your hands are doing, and they stay that way until your next turn.
Say you're a Wizard 6/Swiftblade 3 and you took martial weapon proficiency: greatsword. On your turn, you just take a hand off of your sword to cast whatever spell you want, and then put it back on.
Moreover, a quarterstaff is a double weapon, not a two-handed weapon. The difference is subtle, but you can still wield a quarterstaff in one hand and attack with it just fine. Go read the damn SRD.
http://www.d20srd.org/srd/equi...ons.htm#quarterstaff
And you don't have to take your hands off of weapons or shields in order to grapple someone. You can do it with your hands full. I don't remember exactly what you're talking about with the baron fight, but it might have just been for flavor purposes that I described him taking his hand off of his trident. It was a one-handed weapon anyway; he was simply using it with two for the higher bonus damage on his primary attack. Plus, it looked awesome.
And the baron was, well,
is, by far my favorite mini-boss. You guys let him run away to fight another day.