You're going to have to remove the timing belt I'm afraid as the water pump is partially covered by a timing belt tensioner. It's still a pretty straight forward deal to install the timing belt afterwards (there are pulley alignment marks to set the timing correctly - just make sure the belt goes back on the same rotational way you removed it by painting an arrow on it unless you're replacing the belt at the same time) The RWD engines in Mitsubishis are fairly forgiving to work on (well, most of the time)
Yeah, I hear you when you talk about the stupid stuff manufacturers do when they design an engine. I have a beautiful () 1988 "Holden Astra" (it's basically a N13 Nissan) where GM have, in their boundless wisdom, decided to not only make the water pump timing belt driven but also incorporate it as the belt tensioner mechanism as well. When you replace the belt and attempt to retension it, the water pump body must be loosened off and rotated with some ginormous spanner thing. Once you disturb it, the thing pisses coolant in 17 different directions. Next thing you know, you're up for a new water pump - and replacing this thing with the engine still installed is a freaking nightmare...