Other than acetylene, the only thing that will effectively cut those is a high-speed cut-off wheel. I've managed it with the heavy-duty cut-offs in a Dremel. A high speed air tool would work too as long as you have a disc rated for that rpm. Eye protection, and even hand protection is an absolute must.

2002 X5 3.0 242,000 miles
2004 325i 107,000 miles