A listen to the a capela mix of "Your Imagination" gives us an idea of what kind of production work was done. There's pitch correction in various spots and maybe a plug in added to give even more "layered" effect (layers of layers, that is). However, there definitely seems to be a lot of actual Brian vocals present in the mix. Even some clever bits that are buried in the final mix.
I wouldn't mind having access to the multi tracks for this one. It'd be a lot of fun to mess around with.