is it possible? how?
It depends which ones.
Synths usually don’t support it, sampler vsti’s do, this can be achieved by aliassing.
An example is given here:
http://tutorials.renoise.com/?n=Renoise.UsingVST
Note down the keyword:channel
i think it’s not possible with aliassing…
(with this vsti you also need to change patches with program change or
something i’ll try again tomorrow… hope it will work!)
bytheway: this is the (free!) vsti (even without multitimbrality a very cool vsti)
that supports multitimbrality: