Thanks for the comment. :-)
It looks like it's not possible to trigger one of multiple TH3 Instances without using a Midi Event Filter on the tracks you don't want to trigger.
Alternatively, you could unclick the input echo button on the tracks you don't want to Overdub when you stomp the pedal. This is complicated though. You used to be able to have no midi tracks with input echo enabled, but these days, that's a trick. :-) I don't know how to do it.
So, using the input echo, it's possible to select one or more midi tracks to route to TH3, but it is hard to turn them off. You have to set them to automatic and then click on another track to turn off input echo. This is a two step process.
If you know you'll need it, it might be easier to add a midi event filter and just enable that.