How do they do it in England? Here is an answer I found

"The league below the English Premier League is called the Coca-Cola Championship. The Championship has 24 teams in the league where 3 go up to the Premier League and 3 go down to League 1. The teams which finish 1st and 2nd go up and so do 1 of the teams in the play offs, which is between 3rd, 4th, 5th and 6th."

Not sure who this is worked out in playoffs but I would guess they use a bye week to get to 4 teams and last of 3,4,5,6 standing moves up. (I could be wrong, as my wife often points out to me!)