I take the bolts out completely, insert a pedal spanner in the gap and then screw the bolts in from the other side (need to tilt the saddle forwards to do this). This generally forces the clamp open just enough to slide out the two halves.
Took me a while to figure this out, but the seatpost is about 5 years old, has had quite a few saddle swaps but I haven’t had problems. I might have a look for any stress fractures next time I swap saddles though….
Hope that makes sense. If it doesn’t, let me know and I’ll post some pictures for you….