Spirit Tracks uses 1MB save files, all current hacks and workarounds make it use a 512KB save instead, that is also the maximum space available to the EZ4 for the SRAM (1MB or 8M). The anti-flashcart code stops you from using things like passme. The EZ4 currently only supports a max of 512KB save (that's because of pokemon). If a NDS game comes out and uses something larger than 1MB for save files, it won't matter how much you beg or ask for it to work on the EZ4, it would be physically impossible for you to play without a working save.
It is high time you start using a slot1 to play NDS games. Passme was originally made for NON-SDHC (2GB or less) slot1 flashcarts. If you got a SDHC capable slot1 and still using passme, you pretty much turned into a cheap ass who wont spend 20 bucks or equivalant for a 8GB microSDHC.