Scripting

I assume that you have tried interogating the exe that you are calling for a silent switch command (eg /help /?).
And that you have checked the exe version and googled for cmd extensions.

If you simply cant do something silently and must have GUI interaction.
Then you can write your own uninstaller to do it all silently, and bypass its uninstaller.

Or alternatively you can script against the GUI as a last resort.
With vbscript you can use the sendkeys command.
Alternatively you could use AutoIT

To uninstall an MSI (IF that what you are looking for) is msiexec /x Package.msi /qn, it will trigger a silent uninstall with no prompt.
The X is the command to uninstall

The /q : Silent installation/uninstallation. The installer runs an installation/uninstallation without displaying a user interface. No prompts, messages, or dialog boxes are displayed to the user. The user cannot cancel the installation. During uninstallation, the installer restarts the computer whenever necessary without displaying any prompt or warning to the user

The /qn : Displays no user interface

Hope this help

Sorry forgot to mention if you don't want to restart the PC you will need to use

REBOOT=reallysuppress prior the /qn

and you can also use the ALLUSERS=1 to remove it from all users of that computer.

so hewre the complete command : msiexec /x package.msi ALLUSERS=1 REBOOT=reallysuppress /qn

ALLUSERS and REBOOT need to be uppercase as they are Public Proprieties.

All very useful but you assume that the original install was MSI-based: the OP states that his is an InstallShield-based install. Normally, adding '/s' to the uninstall string will silence IS installations. If it doesn't, then the idea of creating an MSI-based uninstall is a good one. I prefer that to using AutoIt (or similar).