I recommend the turkish cast on
instead. It's really easy, and the tutorial is specifically written for two-at-once socks on ML. Great pictures with step-by-step instructions. The results are beautiful, too.
P.S. To avoid a loose cast-on row that has to be adjusted later, instead of wrapping around both needles when you're casting on, pull the bottom needle out a bit so that you're wrapping around the top needle and the cord
. Since the cord not as thick as a needle, the cast on will be a bit tighter.