Hello all This is a project I have wanted to do for almost three years but hit a bit of a stumbling block I could never find a product that let me mold it to the shape of my ear and would harden without much shrinkage.
Finally thanks to mikey77 and his OoGoo I have a material that not only has all the properties i was looking for but removes most of the building complexities as well

Step 1: You Need

Items you need
Clear 100% silicone
Cornstarch
Earbuds with removable ear cushions
cheap pen
a small drill bit
paper cup
gorilla tape
optional dremal/drill

Step 2: Make Oogoo

for a very in-depth analysis of what Oogoo is and why it works see Oogoo
its a very interesting read
now on to the build
first thing you want to do is make the Oogoo I suggest using a paper cup to mix it in to start as Oogoo likes to stick to its container.

cover the end of whatever you are using to mix with gorilla tape so as to make a spatula shape

add approximately equal parts silicone and cornstarch into the cup and mix it till it starts looking dry enough to touch

Step 3: Knead

put a dusting of cornstarch on your hands and grab a small glob of Oogoo.
start to knead this piece adding cornstarch if you feel any wet spots.

Step 4: Mold

once the Oogoo starts to feel like Playdough stop adding cornstarch and continue to knead it till it begins to set it will begin to get harder to knead at which point you want to take a small piece and make a ball about as big around as a nickle

CAUTION: the following step shouldn't be done by people with sensitive skin as if the Oogoo isnd sufficiently cured you could end up with mild acid burns in your ear (found this out the hard way)
be sure to add a layer of cornstarch around the ball to act as a barrier / release agent
also dusting your ear with cornstarch prior to insertion is strongly advised
and Gently place it into your ear try to flatten it into the little cracks around your ear canal

Step 5: Put It All Togeather

once satisfied with the seal of your new headphones take the ear-buds and remove the original earpiece and push them into the Oogoo make sure to point them into the center of your ear canal
wait about 5 minutes and remove the earphones by pushing the back of your ear and giving a little tug on the earpiece

Step 6: Can't Hear Yet

remove your newly formed earpieces from the ear-buds and drill a small hole from the end of the ear-canal lobe to where the ear-bud goes you just need a pilot hole it doesn't matter if it closes itself after the bit is removed.
put the ear-buds back in the earpieces

Step 7: Sound Tube

take the pen apart and cut off the end where there is no ink.
gently push the tube into the hole you just made and mark where it is flush with the silicone
remove and cut the tube slightly smaller than where you marked

Step 8: Your Done!!

push the little tube into the silicone and enjoy your new custom fit ear-buds

EDIT:The pen tubes can be removed after the silicone is fully cured (I waited about a week) and used to make another pair doing so also allows more sound through