Amy has a video for one kind, at least. I like to just crochet a long chain with some extra, different colored yarn--longer than the amount of cast on stitches I need by a few--and pick up stitches with my main yarn in the back loop of the chain. If it gets crowded, you can skip a link in the chain if you want, and if you don't knit into the correct loop it really doesn't matter either because you can snip it out.
Another way is to cast on as normal with some contrasing waste yarn and knit a row or two before switching to your main color. When you're ready to bind off that end, you can pick up one loop of each stitch with a needle on the first row where the two colors meet. (see 'finding a destination row') Cut off the cast on and rip out the extra yarn and you've got live stitches on your needle.