Anyone using Mac build agent and code signing the output?

We are using TeamCity to build a Mac Cocoa project using the Mac build agent on a Leopard 10.5 box. Part of the post-build script calls for the application to be digitally signed using a certificate in the keychain. We have been unable to get the signing to work so far when it is part of the Mac agent daemon process. Running from a standard dev box works fine. We suspect that this is due to the daemon process characteristics of the build agent but wondering if anyone else has tried this?