There is no wrapper/plugin in
SimPE for the FX internal file format, which is where the effects are located as far as I know, so until someone writes one, creating new effects will be impossible.
(Speaking of which -- does anybody know where to start if you want to write such a plugin, and what are the prerequisite (e.g. programming language) skills?)
Sorry if it's considered a necropost, this might be my first time on the MTS forums.