So the 14,13,13,12,10,8 array is still 23 point buy.
Why not just go with: "27 point buy. You can buy a maximum of a 15. You may spend four points on a single feat, but if you do the maximum you can buy is a 14. If you don't want to choose, use the non-feat standard array of 15,14,13,12,10,8 or...