Is this possible? Because as far as I know all transactions have to be queued and only transactions with higher fees set will be given priority.
A miner can include any tx they want into their block, that's why mining pools run tx accelerating services, if you attached a low fee to your tx and it is stuck, you can accelerate it by paying a service fee to one of the mining pools that run accelerating services and they would add your tx into their block. ViaBTC also offers free accelerating, but it is limited to just 20 slots per hour.
