Hi Rob,
an interesting question, indeed.
Unfortunately, I didn't have a chance to test it yet, but I *think* it should be as easy as using the ashUpd.exe program as the script.
That is, try using something like
<avast-path>\ashUpd.exe vps
I'd be very grateful if you could test it and eventually confirm if it's working or not. If it is, we can create a FAQ entry about this so that other users will be able to benefit from the information as well.
Thanks
Vlk