The only mod I had found thus far for getting a better seal on the AKG K550 was Curly's post here- http://www.head-fi.org/t/613707/the-akg-k550-appreciation-discussion-thread/15
But I've discovered an even easier mod for people who are less keen on bending the holy hell out of the band or stuffing the pads.
The answer is actually ridiculously simple...what is it? Rubber Bands.
I noticed that pushing the cups closer to my ears boosted the level of bass, but greatly diminished the soundstage and made the high end way too harsh. But I discovered that just squeezing the pleather cups a bit while wearing them actually made the K550's sound fantastic (ie the way AKG intended) with nice, clear thumpy base and still a wide, clear soundstage. So with that I found a couple of rubber bands and placed them around the foam cups just beyond the plastic around the driver.
Let me say I have a pretty small nogin, but believe me, it works like a champ. Finally instead of me fussing every few minutes to get a good seal, they sound great as soon as I put them on. The bass no longer feels out of reach and the mids tinny.
As you can see it puckers the pads up just enough for people with small heads to get a good seal. The best part is, I left the bands on for 24 hours and took them off just to see, and the pads just sprang back into their natural shape, so it wont damage your pads.
It may not look very glamorous, but believe me it works. And now I don't have to sell these great cans. I'll probably try to find some black rubber bands to make it less obvious.
Hope this helps some of you small heads out there...