Heat Dynamic Source Location

[MaroisConsulting]

How can I change the location of the Heat -dir at compile time?

Here's my preprocessor variables:
<DefineConstants>Debug;FilesPath=C:\Projects\Acme Widgets\bin;;ProductNameInfo=$(ProductName);VersionInfo=$(Version)</DefineConstants>
I'm passing in the name of the app. How do I specify the FilesPath in the heat command? The release folder under build will be different.