I'm a humanities person, so I can't give you any subject-specific advice...
You may occasionally find a University who'll allow you to submit a substitute personal statement, but they're the minority. I know of some people who've said they've emailed departments to ask if they can, but I don't know whether they've been met with a good reaction- you may be able to find sources online about this?
Thankfully, that was my situation- I applied for a different course at Durham University to all of my others, and was able to submit a substitute personal statement.
Otherwise, I'd advise talking to a form tutor or teacher at your school who might be able to help out!
It's also potentially worth looking around the internet. There are quite a few sources of information on TSR & elsewhere
My common sense would say to try to find similarities between the 2- what are the founding bits of them which appeal to you? Also, it may be worth starting to write your statement earlier than your friends, as it might take a few more re-drafts and more editing as you're attempting a more complex task!
It can be done, though