He mentioned he needs longterm capital losses not shortterm. One option is to lose approximately $8,500 in futures trading which makes (8,500 *60%= 5,100) loss in long-term and the rest of the loss from 8,500 (3,400) a shortterm loss. This is actually easy. Buy really far otm futures options on the day of expiration( doesnt have to be as long as the spread is wide to cause your losses with ease) and sell it back for close to zero. Comms and fees are part of the loss so also factor those in the calculation.
I guess this comes with extra 3,400 unnecessary losses. If you have longterm capital gains that needs to be realized this year, short-term losses can offset some, so you can adjust the needed losses on those futures accordingly. I believe you can use spx options instead of futures as well. spy etf and/or options are a little vague on the 1240 treatment.
Anotther thing you can do is sell 10 /es futures contracts and buy 2,000 spy etf simultaneously and put a oco stop buy order 17 points away from entry price with buy limit order 85 pts away on the es futures while spy etf sell limit order 1.7 pts with stop market order 8.5 dollars away (given that your broker provides 24 hour spy etf trading). This ratio will offset the shortterm losses from the futures through spy etf gains or if the market keeps trending the unintended way, it will give you a gain of 25k ish in total to make it worth it. This comes with market risks during times of uncertainty and gaps so I'm not really recommending but just being crative in response to the question. Just being theoretical.
Do not take it as a serious advice or any guarantees. Just having fun here.
In order to have longterm capital losses that don't already exist in the portfolio, I couldn't really think of anything other than the 60/40 rule to take advantage of for the given same year.