Advanced: How do I use devenv to set a property of the project

I have a setup project which builds my msi. It turns out the ProductCode property of the project needs to be changed on every build to enable it to be upgradeable. Since we have an automated build, I naturally can't do this in the IDE every 20 minutes.
We are using deven which looks like it has options to execute commands in the commandwindow. I am wondering if there is a way to execute a command in the commandwindow to change the productCode property on every build.
Before you recommend it, yes our last resort would be to switch to installshield which does this for you and is much nicer. I am hoping not to though and hoping not to redo this installation work.
thanks,
dean
[708 byte] By [DeanHiller] at [2007-12-16]