Well you can but as a professional grower I will say that the quality of the plants won't be as good. Not necessarily "too leggy" but more leggy. It is the act of transplanting that triggers the development of fibrous feeder roots in the plants. And transplanting them deeper eliminates any leggy development.

But some do it the way you suggest and get away with it. If you don't fill the cell packs more than 1/3 way when seeding then fill it more as the plant grows so that the stem is buried each time you can eliminate the leggy appearance. Won't do anything for the root development though. Your choice.

Dave