You know how boys used to wear short pants and then graduated to long pants when they were fully grown? Why can't we do the same thing with baby clothes? How about pants with snaps down the sides- they start out with a cuff folded up several times and the snaps hold the cuffs up. As the legs get longer you take the snaps down a notch and get a longer leg. You could have some cool, patterned fabric lining the pants.
I haven't bought any baby clothes for Boyo yet because my mom is such a gifted second hand shopper. But if I did it would sure burn me if I bought something that he grew out of after wearing it only a couple of times.