I thought I would let the community know that I reloaded some 450BM today and crimped with my 460S&W Magnum Lee Factory Crimp Die with no modifications to the die. The only "unique" thing that I had to do was instead of inserting the case into the shell holder, I had to set it on top of the shell holder. Worked surprisingly well! It crimped the 450BM cases exactly like I was hoping it would!
At only around $12, it might be worth your try!