Just so that this can be taken off the unanswered list. Like you said, you need to add CODESIGN_ALLOCATE to the $ENV array:
$ENV{CODESIGN_ALLOCATE} = '/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/codesign_allocate';
If everyone is in agreement here, I think this question can finally be closed.
When using a more recent version of Xcode, the default location is:
$ENV{CODESIGN_ALLOCATE} = '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/codesign_allocate';