The language of the law is so clear and unambiguous that...
Oh never mind.
Congress can do away with the 9th and create a different replacement. Trump can then fill it with only his nominees. This can be done with all federal courts except the SC. In the case of the SC, however, the number of justices can be reduced down to one I believe. And the next day increased back to nine. At which point Trump could again nominate eight new justices.
The downside is if the Dems get the house, senate, and executive back they can do the same. But I suspect if they do gain that level of control again they will do exactly that regardless of the actions of the current congress.
Wow - talk about neutering the Leftists ... I love your idea !!!