To support building patches it would be helpful to add the ability to build patches with the InstallShield 2009 Project action. I am currently accomplishing this by shelling out to IsCmdBld.exe. Here's the help that describes the option.
ISCmdBld.exe Command-Line Parameters for a Standard Patch
Parameter
Project Type
Description
-patch_config
Basic MSI, InstallScript MSI, Web
Use this parameter to build a standard patch. Pass the name of the patch configuration in the Patch Design view that you want to build. For example, the following command line builds the patch configuration called Version 1.2 in the MyProject1.ism project: