I was hoping to do the same thing. Some questions I have:
1. We itemize so my state refunds are federally taxed next year. But I can elect to have my state tax overpayment applied to 2018 state taxes and not refunded. Will the state overpayment be taxed federally next year even if I don't get a state tax refund?
2. When I used Turbotax to enter a hypothetical extra state tax payment of 10k for 2017, it didn't affect my federal taxes at all. So I wonder if there's something I'm missing that Turbotax knows.