Unfortunately there is no supported way to do this.
When you consider that the maximum 7-mode ONTAP is 8.2.5, and our current ONTAP release is 9.2, with 8.3.2 the minimum recommended for CFT, there are a number of significant challenges. As a data management company we take the integrity and availability of customer data very seriously, and for a big change like this, we wouldn't want to do anything less than the best.