Default [Q] How to go from dual boot to triple boot?

Hey guys, long story short I'm running a CM10 nightly (10.2-20130925-NIGHTLY-encore) on my Nook Color through SD (also stock on EMMC), and though it works and I like JB and all, JB doesn't support the wiimote for my hardcore gameboy emulation gaming. I'd like to still keep stock on my EMMC, but dual boot between CM7 & CM10 on my SD.
I've read about Racks' method, but don't understand exactly how to get from here to there. Any help/ideas?