Just load the plugin as your play device of choice. Of course the plugin has to be visible for Sibelius in the specific VST folder.
If you prefer an external host, please follow 2 hereabove.
Use the expression tool (Ctr+E) for changing patches: ~C1,value
For example ~C1,0 for the basic patch.
When using the plugin you may prefer an external host and in this case you will need a kind of MIDI routing program. A good VST host is Cantabile (32 and 64 bits versions, audio recorder included). Energy XT is also a fine program for this.
There is such a routing tool for free available, made by Jeff Hurchalla, called Maple. With this great tool (32 bits only) you can use together with your favourite notation program as e.g. Sibelius or Finale.
After installing and rebooting there will be four new Midi ports added to your system: Maple Midi In or Out 1,2,3,4. These ports will be visible in your notation and sequencing software from now on.
Choose Maple Midi In Port 1 and assign the right channels to this device (Maple Midi Port 1) in the Midi out of your notation software. That's all.
64 Bits users will need a cabling option offered by a.o. Nerds.de, up to 30 ports.
If you really want all instruments in one channel you will need a modular solution. Cantabile,EnergyXT are such programs. Also Reaper as DAW will do a great job.
Just load the plugin into your channel(s) of choice. In Overture it is possible to have all instruments in one channel without any effort.
Overture (also 64 bits now in their Overture 5 version) offers a very easy and practical solution for combining patches with articulations or 'expressions'.