The best way for this is avoiding Storyboard.
DVCSs are designed for full error-tolerenceable text based source files. It requires the files are fine to be broken (e.g. for compile). This is the premise to merge data files without any issue.
Storyboard/IB data files are zero-tolerence. They always require full integrity for their data files. As the internal data is described as a interconnected graph, there's no effective way to manage Storyboard/IB data files in broken state. Most data files are in this form, and cannot be used in DVCSs.
Then, trying to use zero-tolerance data in a system which require full tolerance doesn't make sense. At least for merging.