Your broker does not care about your IRS trouble. Something to keep in mind. Just use your broker's December statement to show IRS your open positions at the end of the year. My understanding is that you just want to move amount from Box 8 to Box 10.
No, you misunderstand the problem with boxes 8, 10, and 11. I believe Box 8 should show P/L on ONLY the closed trades, Box 10 should show MTM P/L on ONLY the trades still open at year's end, and Box 11 should show MTM P/L on ALL positions held during the tax year, that is, the sum of Box 8 and Box 10.
But the problem is that on my broker's 1099, Box 10 is zero, instead of giving the non-zero P/L on trades still open at year's end; and Box 8 merely equals Box 11, instead of showing P/L on ONLY the closed positions.