A friend of mine who is a bunny-lover as well as a certified master herbalist recommended the pumpkin seeds. She said that they help with flushing calcium out of the system. I have no idea what is in them that would do this. I'm just taking her word for it.
Another friend's bunny was experiencing sludge and had to undergo bladder flushing every few months. She started giving him pumpkin seeds and he was able to go 2 years without needing another bladder flush. She thinks that the pumpkin seeds helped him alot.
I have a veterinarian friend who is very experienced with rabbits and he maintains that the intake of foods high in calcium has no effect on whether or not the rabbit develops sludge. It's more a matter of how well the rabbit's digestive system deals with calcium, not the amount of calcium. Nonetheless, if I had a rabbit with calcium issues, I would delete as much of the high-calcium foods from the diet as I could.
So, really, all I have to offer is what other, more knowledgable people, have told me.