I'd just bought some great SuperFi series earphones from Ultimate Ears, but I found that the ear tips they provided, while they were pretty good, were not quite as comfortable as Shure's triple-flange ear tips. I ordered some extra ones from Shure, but found to my dismay that they did not fit onto the plastic tube (from which the sound comes into the ear) of the 'phones.
After a few simple cuts on the ear tips (DO NOT CUT INTO YOUR EARPHONES) and a bit of pushing, I found that I could force them on.
As I seem to have narrower ear canals than Ultimate Ears envisioned, the noticeably smaller Shure ear tips felt much less than a brain probe, while still maintaining a proper seal and a comfortable fit. I noticed that someone on ebay was selling triple-flanges that seem to be modded with a receptor for a larger tube, but you can take your own chances with them.
Step 1: What You Need
1. The Shure triple-flange ear tips
2. A very small pair of scissors (like a nail scissors... I used a swiss army knife scissors)
3. The will to succeed
Note: the silicone is pretty resistant to cutting with a knife, stop being lazy and go find a pair of scissors.
Step 2: Procedure
1. Take the 3rd (the largest) flange of the ear tip and fold it back over the 2nd, exposing the silicone tube.
2. Cut off almost the entire the silicone tube, leaving just a millimeter or so of it left protruding from the inside of the 3rd flange, enough to make a little lip to go over the earphone's plastic tube.
3. Make a small cut at the North, South, East, and West point of the little lip that is left, cutting only slightly into the material behind it.
-Be careful, cutting too far will rip into the flap of the flange itself
4. Use your thumbs and forefingers to stretch the opening. You should see four equal sections of the lip stretching outwards.
5. While stretching, push the ear tip over the plastic tube of the earphone. This will not come very easily, but you should manage it with a little effort.
6. Repeat for the other ear tip.