No Easy Way
I'm not sure why you think 1500 hours gives you a get out of jail free card. If you did have an FAA ATPL, all you could get out of is the CAA's 650 hour study time requirement. It is not possible to sit the exams without a registered training provider putting you up for them. In other words, you could enrol on a distance learning course and do whatever study you saw fit instead of slogging through every last frame of instruction and every progress test. The catch is that all of the schools wish to protect the grade point average of the people they put up for the exams, so they will still require you to take some school tests before they will sign you off as ready for the JAR exams. The CAA hold the schools accountable for their GPAs and the schools won't sacrifice this statistic by throwing your name in the hat willy nilly! It seems like a bit of a racket, but it's hard to argue it's not in the public interest.
In your case, since you don't have the FAA ATPL, you'll have to do the entire course either by distance learning or by sitting in a classroom for 6 months or so as no school can legally waive the 650 hour study requirement, 10% of which must be done in a classroom.