I found this website with tips for increasing water consumption: http://cl-ruth.s-ivil.tripod.com/id8.html
One of my favorites is to use the "juice" from a can of unsalted salmon or tuna, diluted about half and half with plain water. You can keep topping up the can with more water and store it in the fridge for 2 or 3 days to get the most out of it.
Also 'Baby Food Soup' works well. Plain chicken (no onions) mixed with plenty of warmish water is a big treat for my kitty.
I understand not wanting to do subQ fluids just yet, but if it ever does become necessary, it's not so bad if you follow a few tricks (like warming the fluids first, using a higher gauge needle, giving lots of treats, etc). In fact, I'd way rather give my cat subQs than anything orally! Many cats learn to associate the procedure with feeling better and become quite compliant about the whole thing. I have lots of links on subQ stuff if you ever need them.