My Fed'l form correctly recognizes a backdoor IRA contribution, as such. The nj 1040NR sees it as income in columnA. How can I get turbo tax to remove it from the form?

As you prepare your NJ return, you'll see a screen  Roth Conversion For You. If you had no other traditional IRAs existing before or after the conversion, you would enter the amount of the distribution as Contributions Relating to This Distribution Previously Taxed By NJ. See the screenshot below.