Hi folks,
I just figured out how to switch Multis through MIDI Program Change messages from Cubase LE, so thought I'd describe it to save other noobs like me, a bit of time.

Of course, it might be slightly different in other sequencers, but I hope this should help get you on the right track, anyway!
On the TI:
1. Edit Config MIDI 1/3 MIDI Global Channel to be something you aren't already using for parts, such as 16.
2. On page MIDI 3/3, make sure Multi Prog. Change is Enabled.
In Cubase:
1. Create an empty MIDI track and assign the output to MIDI channel 16. (Or whatever you set on the TI.)
2. Create a small MIDI part at the start of the track. (I just recorded a few notes, from my MIDI keyboard.)
3. Open the List Editor for the track and remove the notes, or any other unwanted content.
4. Add a Program Change event at the start of the list. Set MIDI channel to your chosen channel, Data2 value to 0 (the TI MIDI CC number for Program Change) and Data1 value to the required Multi number. The Multi numbers starts at 1 and can go up to 64. For example, I wanted to start the track using Multi 2-1 on my Snow, so I used 9 as a value.
5. Add similar Program Change events, whenever you want to switch to a different Multi.
Anyway, I hope that saves someone some time!
In my case, I'm still working on my covers of Blue Monday and Bizarre Love Triangle and have (quickly) run out of parts. I've got another synth module coming soon, but in the meantime, I'll just switch between a few different Multis, so I can change a few lead parts at a time. Really gotta have those vocoder parts in there, so I had to find a way!
Cheers,
EG