Finally got it on my 3rd attempt.
What I did was beat my first opponent until I had 3 finishers stored. Then keep beating on him until you earn another signature, hit the Chokeslam or Last Ride then pin him. For every other opponent I simply waited until they got into the ring and hit the Running DDT (LT + A) then stomped them until they got up. Running DDT again, stomp, rinse and repeat until signature was earned. If you run into trouble use a finisher in the beginning and wait until you've earned a signature before pinning and moving onto the next guy so you always have 3 finishers stored.
When you get to 45, Running DDT from the start. If you get reversed don't panic, go for it again then hit your finisher. Stomp on them and Running DDT until you earn your signature. Then use your signature and pin. You're back at 3 finishers. Do this for every single person after 45 and you should be fine.