Saddle suggestions for broken pelvis
You may try looking into a noseless saddle. Some of the designs I have seen actually have cutouts or the sit bones in particular. Many people are dismissive of them (myself somewhat included), but they may hopefully be an alternative for you. Here is a completely random blog entry on the interwebz comparing several. There appears to be a large range of manufacturing quality as well as actual design effort, so I would resarch rather carefully before purchasing.

I would also strongly look into an alternative fit of some sort. Perhaps a more aggressive position that placed more weight on your hands (or other slightly non-traditional fitting) would be of benefit.  Professional fittings should always be looked at as a place to start.  Especially with past injuries or other less stereotypical anatomy, minor or major adjustments should be expected.  In the end it may not be one thing, but a combination of things (including perhaps time) that help things along for you.