I think they'd do it in a similar way to how they deal with business interests for politicians. They'd set up some sort of blind trust, where City Football Group are the beneficiaries, but where the trustees hold the rights to vote on any shareholder business. At the end of the season, unless they both qualify again, the trust would be wound up and City Football Group acquires the voting rights again.
The point of such a structure is that it doesn't trigger a disposal of any value (since City Football Group still has the rights to profits) but it ensures they can't control both clubs. This will probably avoid a disposal for either tax or accounting purposes. I think, as has been said for Red Bull, that they'd also need to prove separate, independent management of the two clubs, which may mean they need to tweak the boards of directors.
And on that point, there is a suggestion that the United situation may be a little more complicated than I originally thought. Although Ratcliffe owns less than 40% of the shares, because he has control of football operations at United they may need to prove no shared management with their French club as well.
