I've found a couple things that help at our house, but maybe it's coincidence or luck.

I'll list them anyway in case they do really help...

Grass: I find that clipping the grass to about 1 - 2 inches satisifies the cats and cuts out barfing/grass in nose factor. (Or maybe it's coincidence that it works for us...)

Cat treats: All our cats love the Pounce brand cat treat, but when they were kittens they needed to be limited to only a couple a day. I was told that these treats have a lot of salt and sugar in them compared to standard cat food and are too rich for kittens on a regular basis. (On the other hand, I'm unfortunately gullible when it comes to cat info.) But the cats can handle much larger inputs of Pounce now that they are older without upchucking, so it could be true.

Hope this helps!