Hindsight is a wonderful thing.
The problem was that the money to buy the slaves from their owners was seen before the war as impossible to raise, most historians today would agree with that but the actual cost of the Civil War was much higher.
Let say a plan is offered to the slave owners, that they could if they agreed to a generous package to convert their slave plantation to sharecropping over a long period of time say 30 years. For their loss, a large compensation would be agreed.
Do you think enough would agree to make a significant difference?