Enable binary custom rules

[rjmholt]

PR Summary

Looking through the code, most of the existing code was already there to support this. So I've just hooked up the final piece.

PR Checklist

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• Summarized changes
• Change is not breaking
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[bergmeister]

Not too surprising, I remember this comment from the previous maintainer: #765 (comment)
In the first instance, if getting it to work is that simple, then I'd say writing an automated test could even be deferred to another PR as I can understand this would be more involving, especially since Ps Core cannot unload loaded DLLs easily

[rjmholt]

For an example of how to implement a binary rule with this change, see this gist

[bergmeister]

@rjmholt If this PR makes it work then I'd be happy to just merge it and we can raise a backlog item for writing a test?