Mulitple paths in - upgrade issue

We are running on 1.7 and plan to upgrade to 2.2. Our has 2 directories in it. In testing upgrade, it took 10+hours to complete the upgrade of 8 data nodes with 1TB of data.
I read about 2.0 breaking change when it needs to move all the files belonging to the same shard to the same path.
I was thinking we could go back to using 1 path temporarily (plenty of space, using only 1% disk on each path), while we are in 1.7. Then upgrade in timely fashion, and then add the other path.
How would we go about changing from 2 directories in 1 while on 1.7? Am I looking at the same process of 10+ hours of moving files around? Is there some workaround?