As a retired teacher I used an interactive whiteboard every day. I was also responsible for trainee teachers and find it absolutely unacceptable that you have not been given access to a laptop to be able to project your PowerPoints. At the very least you should be able to use the laptop of a teacher in the subject department to which you are attached.
Have you spoken to the IT Department, your Mentor, the Head/Principle?
Some projectors do have a bluetooth facility to enable some tablets to be used to project to the whiteboard but that would mean changing settings on the projector which, in the circumstances, I'm not at all sure that the school would be happy for you to do.
Before you go down the route of trying to adapt your tablet you really should try to get the school to allow you to use one of their laptops.