How to select which instance to update with command line ?

Hello,

I have an installscript project (non MSI), which is in multi-instance mode.
In most cases, the setup.exe will be launched from command line in silent mode.

Then, new versions of the program will be generated, and we may have to update som instances that are already installed on the machine.
The problem is that i don't know how to select which instance I want to update from cmdline (in silent mode).
Is there a way to do this ?