You have no choice about how capital gains and losses are treated on your tax return, or how and when capital losses are used to offset capital gains or other income. There is only one set of rules in the tax laws. You enter your gains and losses in TurboTax, or any other tax software, and the software does the calculations according to the tax laws. There are no choices or options.
I don't understand what you mean by "unused long-term capital gains." Gains are not "used." All gains have to be reported in the year they occur. Any gains that are not offset by losses get taxed that year. There is no carryover of capital gains.
