Late resolution of MSI variable for part of install folder path

Question

In a setup project, on User Interface, I've created a RadioButtons (3 Buttons) dialog box.

I've placed it before the Installation Folder Dialog.

I wish to incorporate the value selected in the RadioButtons dialog as part of the Installation Folder.

To do this I've placed the name of the variable amongst the path where I wish to use it in the DefaultLocation:

  [ProgramFilesFolder][Manufacturer]\[ProductName]\[BUTTON3]

The effect of this is that the default value for the variable, BUTTON3 in the example above, is resolved as part of the folder, not the selected value.

Anybody know how to make this variable use delayed expansion in some way to get the selected value?