You can actually put a nan into a slot.
first thing you should do is to read up on this app in the directions.
some tips though, make sure when you are in the app and on the phone rom and on that 'page' of the app, that you do the setup phone option. That makes it so you can go into recovery and flash a zip and get back to your real phone rom if things go south on you. Otherwise you can just do it from within the app itself.
Flashing these slots does NOTHING to your phone rom, it is sitting there fat dumb and happy through out this process. you might need to flash the zip you would find in the bootmanager folder for phone rom if the slot doesn't turn out though.
another thing you should do is go into menu and check to have screen on during install. That way if you have a screen off profile that your phone doesn't screen off and slow way down.
Now the nand that you want to put in a slot, you get to the slot you want to put the nand in, install zip and and then use the restore nandroid option.
about this nand you want to restore, it should not be of a partitioned rom that is using a2sd or that uses apps2sd to move parts of the rom to the sd card, that doesn't work.
Also, be really patient with it when it boots up, let it have some time to find itself, so to speak.