...I tried to research and can't find any way to do that in any of the exchanges I use such as kraken, bittrex or coinbase.
...So, I am just wondering is it really possible to take profit without reducing bitcoin holding? Am I missing something here?...
In this case, it would be useful for you to get acquainted with the actions that Binance conducts. Now on the exchange, the farming of the Bitcoin Standard Hashrate Token (BTCST) token is available, for which you need to place your BTC for a period of 30 days in the launchpool:
https://launchpad.binance.com/ru/launchpool/BTCST_BTC Of course, you will not double your BTC, but in any case you will get passive income.