He could use his intelligence to manipulate Kate. Maybe he convinces her that he is more useful to her if he is free, and she lets her guard down long enough for him to make a run for it. Also, he could have some hidden skills or knowledge that he uses to break free. Say he knows a spell or a code that unlocks his restraints or the door to his prison.
His father could be one of the supporters. His father has always been there for Stiles, and he would understand if Stiles was standing up for what's right within the pack. Another possibility is Lydia. She's a smart and powerful character herself, and she might see the value in Stiles' actions and support him.
One possible interpretation could be that it's a fan - made story within the Teen Wolf fandom. In such a story, the 'in heat' concept might be used to create a more intense and hormonally - charged dynamic between Derek and Stiles. It could involve a lot of emotional and physical tension as they navigate their relationship in this rather unique situation.
Edward is a popular character to pair with Stiles. Their personalities are quite different, with Edward's brooding nature and Stiles' more energetic and sarcastic self, which makes for an interesting dynamic. Another popular pairing is Stiles and Jacob. They could bond over their experiences with the supernatural and their protectiveness towards their friends and loved ones.
There could be a tough drill sergeant who acts as a mentor and a source of conflict for Stiles. This character would be strict but fair, and would push Stiles to his limits.
Stiles might initially be shocked. He has been a part of the pack for a long time, and Scott kicking him out would be completely unexpected. He could stand there in disbelief, unable to process what has just happened.
Another possibility is that Stiles is there because of a sense of obligation. Perhaps Peter has done something for Stiles in the past, like saving his life or helping him out of a difficult situation. So, Stiles feels like he owes it to Peter to visit him in the hospital and make sure he's okay.
In many 'Stiles is not human fanfiction', Malia could play a significant role. Given her own complex backstory and her were - coyote nature, she might be able to relate to Stiles in some ways if he's not human. She could either help him adapt to his new state or be in conflict with him. Kira could also be involved. Her kitsune powers and her kind nature might lead her to try and understand Stiles. And the Sheriff, Stiles' father, is bound to be in the story. His relationship with Stiles would be put to the test as he discovers his son is not what he thought he was, and he'd have to deal with his own emotions and the potential danger that Stiles' non - human nature could bring.
Scott would be the most likely one. He's Stiles' best friend and the True Alpha. He would never let the Alpha pack harm Stiles and would go to great lengths to rescue him.