If not, give me a week or two and I'll provide something.

There might be something in the actual HISE snippet browser too.

This is called multi-timbral, rather than multi-output. Although they are semi-related.

But basically... each one of those buttons activates a panel where you can access a unique instance of a synth or a sampler, or whatever. So in effect... if you want multi-timbral support, you add as many samplers or synths as you desire, and then you use midi processing scripts to control the flow of data between them, as well as showing and hiding sub-panels in your UI, where each sub-panel corresponds to a range of controls for each synth/sampler.

Basically, think of it like building multiple engines within a single plugin. It isn't a trivial thing to do, but definitely possible within HISE.