What you can do is create a c/c++ program which generates a file Version.wxi
which looks like this:
<?xml version="1.0" encoding="utf-8"?>
<Include>
<?define ProductVersion.Major="4"?>
<?define ProductVersion.Minor="4"?>
<?define ProductVersion.Revision="8"?>
<?define ProductVersion.Build="33"?>
<?define ProductVersion="4.4.8.33"?>
....
</Include>
Then you can include and use those version numbers in the main wxs file:
<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<?include Version.wxi ?>
<?define UpgradeCode="GUID"?>
<Product Id="*"
Name="$(var.ProductName) $(var.ProductVersion.Major).$(var.ProductVersion.Minor)"
Version="$(var.ProductVersion)" Language="1033"
Manufacturer="$(var.Company)" UpgradeCode="$(var.UpgradeCode)">
Generate the Version.wxi just before you compile your wix project. For example modify the .wixproj file to add a target which does that.