[darwinbuild-dev] Build configuration

Does anyone know, is there a way to set the build configuration of a project in darwinbuild? The relevant flag to xcodebuild is -configuration. In particular, I'm trying to build zfs under darwinbuild. For Leopard, this has to be compiled with the "Leopard_Release" configuration. I was unable to figure out how to force this setting, though it does build correctly within the chroot if xcodebuild is invoked manually... Thanks in advance!!