that is a little more complicated than it sounds. just by increasing the sidewall size, doesn't mean you will fill up the wheel well. it will also raise your vehicle ride height as well. i could explain more in person as my febble mind cannot put it into words.
the only way I suggest going, is finding out what tires cam one the vehicle originally. find the circumference of the tire. say 50" for example. then find a tire that fits your 17" wheel that has the same circumference. this will ensure proper speedo functionality and accuracy. then equip your vehicle with a lowering spring set in order to drop the vehicle towards the tire, thus filling your wheel well gap. then align it and VIOLA!