I would just throw a tighter cassette on there. If you can give up your 30 tooth low gear, maybe a 12-28, those are easy to find. You didn't say how many cogs you're running, but it's basically a matter of figuring out your lowest usable low gear, and highest usable high gear, then let the chips fall where they may on the gears in the middle. The closer together those two numbers are, the tighter the middle gears will be, and that's what you want.

Or if you know the precise sprocket teeth you use the most, build your own cassette. I have one that's closely spaced on the middle gears up to a 24 teeth, then I stuck on a 32 tooth emergency bail-out gear for when I die on climbs. Manufacturers won't sell a cassette like this because it looks kinda funny, but I find it practical.