The problem with whey + casein is not just the speed of digestion, but the associated insulin spike which is probably brought about by their high BCAA content, which are amazingly insulinotropic while having no effect on blood glucose.
That's not to say that these two products are bad; I use whey everyday, but it's wise to try to prevent the insulin spike, (except pwo which is when you really want insulin).
Ways you could do this:
1. Take with some olive oil; slows gastric emptying + another reason, (which I've forgotten...but it was something to do with receptors...I'll find it later)
2. Take after a meal; the food acts as a buffer
3. Take with fiber; acts as a buffer again + does something else...(I've forgotten again

)
I know that ironaddict, (founder of ironaddicts.com and a long, long term whey user) has recently stopped using whey + started on egg white powder, and has some of his clients do the same, with resulting increases in energy. Whether this has to do with allergies to something in the whey, or reducing insulin spikes, who knows. But I know that when my whey runs out, I'll be testing out egg protein to see if it makes a difference, while still using whey pwo.
But yeah, don't want to scare anyone...the point of this post it basically to say; try not to take whey on its own on an empty stomach.