Basically what you would have to do, is put it in your card reader every time you wanted to switch saves. Then rename the save you wanted to use back to *rom name*.savwait so u tried this on the r4 and you had to re name the save files?
So much wasted space...Nope much easier than that you just have multiple copies of the game, in with a different name. Ie... Pokemon1.nds, pokemon2.nsd, pokemon3.nds etc... each will then have its own save pokemon1.sav etc