I am not going to answer your question directly. The way distributions work from Roth IRAs is that there is no tax until you have withdrawn all your contributions. If you converted any traditional IRAs, the conversion contributions are distributed next. After all the regular and conversion contributions are distributed to you, only then do withdrawals come from earnings. These withdrawals are free of tax and penalty if you are over 59.5 and at least five years have passed since you set up your Roth.
So, without looking up the 72t substantially equal payment rules, my guess would be that for most everyone "substantially equal payments" of the earnings would be irrelevant because of how distributions work.
It is possible that you could, after using up your contributions, take 72t distributions of earnings, but I would check publication 590. http://www.irs.gov/pub/irs-pdf/p590supp.pdf