So I've been working on a (secret) Headless version of DS, and, as you might imagine, it does contain support for program change message. I'd be happy to add this functionality into the real, full plugin as well, but I have a question for you:
Because each Decent Sampler Instrument can contain any number of different presets, I actually have the PROGRAM CHANGE "BANK" control which instrument is loaded and have the actual PROGRAM CHANGE control the internal preset. Would this be useless for you?