Since third-party sick pay is not supposed to be reported at all on the NJ return but ProConnect Tax, by default, flows the amount to NJ-1040, here's what you can do:

1. Go to the input screen for the W2 in question;
2. Scroll down to the State and Local section;
3. Enter -1 in the numeric field (for $0, Lacerte/PTO-speak); and
4. Select NJ for state sourcing

This will keep the third-party sick pay on the federal return but won't flow it to NJ-1040, Line 15.

If yours is a NJ-1040NR, a couple more entries will be needed to make sure adjustments are made to both Columns A and B.  Please come back if that's what you need.