I always guessed those kits were designed for BIAB style brewing. You could do a no-sparge BIAB all grain brew and do it all in one kettle. Just put all the sparge and mash water into the mash and put the milled grain in a nylon strainer bag. Put the bag in the grain and steep at whatever temperature the kit says for an hour. Pull the grain bag, dunk it a few times to rinse off the grains, let it drain out and then discard the grains. You're ready to start boiling.