This is a great question/discussion. 

I'm very curious : several state tax calculations are tied to federal AGI. In these cases, is the best approach to simply exclude the income reported on Schedule NEC of a 1040NR on the state taxes since it is was not included in the Federal AGI?

I understand if the income was earned, it should be taxed at the state level, however, FDAP income like dividends, capital gains etc reported on Schedule NEC of a 1040-NR for non-resident aliens is extremely hard (next to impossible) to account for on state returns (especially states that use federal AGI as their starting point). 

Would love to hear what the fellow tax preparers are doing when faced with such situations.