Chrissy, he needs a block to start from.
I've done it. In 1.4.7. With no angel block either. I just used MCEdit to place a sinlge block in the SuperFlat world and it works beautifully. In unleashed it's even easier. Simply make the world, give yourself an angel block, right click with it and bam. Instant starting block.
And as far as the superflat seed goes, Simply remove all of the layers. The generator will automatically make a layer that is pure bedrock. Simply replace the ID of bedrock with a 0 and that layer will be air, making an infinite void world.