Double premove?

Well you can actually already do a 'double premove' - premove something, then pick up a piece and prepare for it to be put down. After your opponent moves your premove will activate and then when it's their turn after that you drop the piece, thus effectively double premoving.

So basically you premove and prepare to premove again, and after they move it will be their turn again after your premove activates. So then they think about their move while you now premove the original 'prepared' move, premoving twice. Kinda slow but definitely useful.

Please tell me if any clarification is needed. Or, watch a Streamer's Ultrabullet games to see how they do it.

That's not a double premove!

With real multiple premoves on other sites you can make several moves all of which will get automatically activated without any further action needed. Obviously if any of them are illegal due to changes in the position the chain of moves stops and user input is needed.