Software Deployment

If I have an MSI containing a ComboBox control which is dynamically populated with values at runtime, is it possible to use an MST file to select a specific value that you know will always be present in the ComboBox?

Specifically, the MSI I'm trying to transform does a scan for older versions of the software and adds them all to a dropdown list, from which you can choose a specific version to copy the preferences over from. It looks something like this:

Copy settings from previous version:

Please select... ▼
Version 3
Version 4
Version 5

I already know which older versions it's going to find on our workstations, so I want to have it always copy the settings from the latest version, i.e. Version 5 in this example.

I know the ComboBox is linked to a property named ComboBox_Previous_Version_List (presumably populated by a CustomAction), so I tried adding that property to my MST with a value of "Version 5" but it doesn't appear to have any effect.

Is this just impossible to achieve?