Ok I must comment...and sorry if I'm late with figuring this out, but:
Ok with the new 1.1.2 ability to play (<=30 second) custom ringtones, I decided to try something.
I took a full .m4a file (.mp3 works as well), that I had in my iTunes library. Nothing special...just a song from a CD I ripped. Anyway, so there was a specific starting point in the track that I wanted the ringtone to start at. So what I did is:
1.) Made a copy of the .m4a file, and renamed it to something else.m4a.
2.) Then I played the new track in iTunes to find the spot (in time using the meter on the top of the iTunes window) where I needed the ringtone to start. It happened to be at the 0:27 spot.
3.) Then I went to the track info and changed the start and end of the track to 0:27 to 0:57 (30 seconds), removed references to the album name/track number/part of a compilation checkbox/etc, titled it the way I wanted it, and saved the file.
4.) Then I did another: "convert to .aac" on the modified file.
5.) Then I browsed to my file on my computer, changed the extension to .m4r, added it to iTunes, and synced to my iPhone.
Bingo...instant fully-customed ringtone all through iTunes.
I love this 1.1.2 update!!!
Ok I'll stop my rant...