As I was posting on RC I felt silly about asking for 30" T5's. Do they even make them in that size? The only 2 tanks I can think of that are that long are 29g and 20L tanks, so I wouldn't be surprised too much either way.
If you have a 30" tank go for 24" bulbs, that leaves 3 inches on either side that's uncovered but that's ok you'll still get light there, and you really don't need to grow corals against the walls
Also if you're doing some sort of retrofit you can always stagger the bulbs if it's that big of a deal, but then each staggered bulb is 6 inches away from one side