Since I posted that query back in October, a colleague who has seen the draft rules for the Graduate route tells me that, if they understand correctly, the Graduate route appears to not allow self-employment anyway.
If that is what the final Rules for the new route say, my question is moot.
No, I don't have a copy of the draft rules, nor do I know anything else about them.
I do not give immigration advice. I refer you to Immigration Rules, guidance, other online content and to your sponsor.