You can work around this.
Make your first animation with PI and Blocker.
Make a second animation with the blocker moved 1 or 2 or more pixels in the feathered direction you want.
Make a third animation moving the blocker further again.
Three is the minimum, you can use more.
In a NLE or post prod app like AA you can layer the 3 animations giving the layers different transparencies thus creating a feathering of the blocker.
Some trial and error is required to fine tune this process.