sunspark,
I don't believe that is a parameter for an msi transform, but with PowerShell you should be able to do something like this. I think I found this answer at AutoIT when I had a similar question.
Typical powershell installation script steps:
1.Invoke-Item ‘C:\Script\somefile.exe’
Run given app (also .msi).
2.Select-Window PROCESS-NAME | Set-WindowActive
Set focus on the installer window, so you are able to send simulated keys to the installer.
3.Select-window PROCESS-NAME | Send-Keys “{ENTER}” | Send-Click
confirms given screen.
4.Select-window PROCESS-NAME | Send-Keys “{TAB}” | Send-Click
switches tabs in a given window.
5.Select-window PROCESS-NAME | Send-Keys ” ” | Send-Click
activates/deactivates active option button.
6.Select-Window PROCESS-NAME | Select-control| Send-Keys “123456789 1234” | Send-Click
gives you the method to fill textboxes.
7.Select-window PROCESS-NAME | Select-control | select-control -title “CHECK-BOX NAME” | Send-Click
The part which you are interested in is point 7. You need to know the checkbox name and then you can send click command to it.
Thanks,
TE