Don't talk about PRUs like they're a terrible thing. I worked in one and it's the best job I ever had. The staff and students were really something special and the environment was far calmer than any mainstream school I've worked in.
I loved eating in the dining room, just to chat with the students, who obviously all had their problems, but they were so sharp.
We couldn't and wouldn't claim to 'save' them all but they really did get good support and we often got letters or visits from adults living good lives, who felt we'd been the thing that helped them turn things around.
It's true they didn't often leave with good qualifications, but the aim was for them to leave equiped to deal with what came next, to do the work to get them in that place, rather than focus on academic studies, and usually a college or apprenticeship place.
OP, if you think AP will help, it might be possible to "convert" the PEx to a short term placement (often extended), depending on your LA .