How do I force Xcode to link to a custom version of a system framework?

I have a project that uses OpenAL. The project is built against the 10.5 SDK, and the version of the OpenAL.framework in 10.5 causes some problems. I want to link to a custom-built version of the OpenAL.framework that resides in my source tree.

However, Xcode resolutely refuses to do this. No matter what I try, it insists on linking to the framework located at /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/OpenAL.framework/OpenAL. Here are a couple of things I've tried without success:

• Set the path to the framework directory in a variety of ways (relative, absolute) using -F.
• Pass the linker the -Z flag to eliminate default link paths, then explicitly pass /System/Library further on in the link process, to ensure that it sees the system paths after my custom library path.
• Build my library using a prelinking pass, and explicitly pas开发者_运维知识库s the library inside the framework to THAT.

According to man gcc, passing the -F parameter should be sufficient to ensure that a link path is searched before the default paths. Either this isn't happening correctly or I'm misunderstanding the problem, and it seems too simple and obvious to be a linker problem :-)