Is there a mechanism to allocate an earn-out in a sale disproportionately amongst the selling shareholders and still have it treated as capital gains?

For example: Two sellers A and B, each a 50% shareholder, but we want 75% of the earn-out to go to seller A and 25% to seller B.

Also, what fiscal year would the earn-out be taxed based on? i.e. suppose the deal is done this year and the earn-out is paid next year, and that there is also a tax increase next year, which tax rate is the seller paying on the earned portion of the deal?

Thank you.