How can I add a specific card to second half of deck

Hi all, I’m trying to create a game where the players need to draw cards each turn, until a special objective card is drawn, which signals the end game. Is there a way to achieve that, or automatically add the card to the deck once it has reduced by half? I apologise if this has been asked before. I searched a few times but couldn’t find anything.

There isn't a way to model this mechanic on Roll20 currently.

You could 'hack' it (loosely) by having a companion rollable table... once the deck is half gone you'd take cards as normal but also start rolling on the table which would be weighted so that the chance of the objective card is the same as it would be for realsies... it's messy and overly complicated but it would work...  ¯\_(ツ)_/¯

That's a good point. With the API (a Pro Subscriber Perk), you could monitor the drawing of cards and randomly rewrite a card that is drawn after half the deck has been taken. For that matter, an API script could rewrite the cards after being shuffled and swap the special card somewhere in the lower half of the deck.

Thanks for the responses. I was looking at the Rollable tables option, though it appeared that the weighting would need to be changed for each additional card that was taken. (I could be wrong there, as I haven't used rollable tables that often.) The API option looks like the way to go, though I will need to run through a lot of tutorials first to figure out how they're done :)