I filed deeper channels, mostly on the top where the buttons slide but also at the opposing side. It seems like it would weaken the holder but if you don't go overboard it's not a problem. I also needed to remove the angled guides where the edges meet the flat part. These are the parts that press against the long edges of the back of the phone (up close they look like two short, extremely wide stairways). Luckily the flat backing itself didn't interfere.

I'll emphasize that it came out looking really ugly in my case and wasn't worth the bother. The plastic is extremely tough and hard to remove, let alone get smooth. Also I chewed up part of the invis. shield by repeatedly sliding the phone in to test the fit.