One simple approach is for PL to earn explicit cred for supporting SourceCred (e.g. since I am being paid by them to work on it, some %age of all the cred I earn goes to them). Then they could also get cred from the OKR process b.c. they set it up, etc. (Challenging question of how to value the OKR process. 
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If we do go with the “employer takes %age of cred” model, the employee should always be allowed to walk, and contribute on their own (and keep all their cred). Although that woudn’t change the distribution for old contributions.
The support would be in the form of mentoring, connections, and cred. I like your SourceCred treasury suggestion a lot, so maybe before too long we can set up a solid pipeline for money->cred.
I agree with @BrianLitwin that your contributions here on the Discourse are quite valuable, so in that sense you are already earning cred, we just haven’t been able to formally recognize it yet.
to be truly expressive (and therefore equitable), messier human inputs will need to be captured. Yep, keep your eyes out for whatever comes out of the odyssey hackathon. Current brainstorming.