Build a better one yourself? I'm tired of eating.
I am tired of eating too, and have looked seriously into building it myself. It's not clear yet whether doing it myself is worth the additional costs over outsourcing it to him; I think I can do significantly better, but doing it right is a significant amount of work.
Post your superior recipe to /r/soylent?
Rob Rhinehart's food replacement Soylent now has a crowdfunding campaign.
If you're interested in one or more of these benefits, send in some money! There is also a new blog post.