First things first:
Flash guns contain capacitors and can store a huge amount of energy, even after the batteries are removed. This energy can cause serious injury or even death! Do this mod at your own risk! Please be careful.
Basically, this mod will allow you to sync your YN-460 without the use of an add-on hotshoe/pc adapter. If you use Pocket Wizards, this mod is a must but even if you use rf602's or the new phottix atlas triggers, both of which have built in hotshoes, this mod will allow you to bring the flash closer on axis to an umbrella or other light mod. Better yet, because the sync port is a standard 3.5mm jack, it allows you to use inexpensive headphone extension cables as sync cables. Pretty sweet.
You only need basic tools to do this mod. A cordless drill or dremel tool with a drill bit just slightly larger than the outer diameter of the 3.5mm jack, a soldering iron, a spool of fine electrical solder, a wire stripper, and a small Philips screwdriver (not pictured). In addition to the tools you will need a 3.5mm mono jack...
...and a short section of two conductor wire. The gauge of the wire is not really important, but it should be big enough to be easy to work with but small enough that it is easy to bend and shove up into the body of the flash.
Take a look at the contacts on the 3.5mm jack. It may help to insert a 3.5mm plug to see which contacts match up with which solder points. Tin the solder points on the jack and solder the red wire to the "tip" solder contact and the black wire to the "sleeve" solder point. You will notice that there is an extra solder point in the photo above, this is because I used a stereo jack and the extra solder point is for the "ring" contact. If you can't find a mono jack, just use a stereo jack and ignore the ring solder point like I did.
Next we will be taking apart the flash. The photo above shows how the the hot shoe is attached to to the flash body. simply remove the four small philips screws and the hot shoe will pop right off. Be careful not to pull out the 2 small wires that provide electrical contact to the hot shoe.
Next you will have to push in the two small tabs hidden under the flash head. I did this with a screw driver, be careful, I broke one of the tabs on each of the flashes that I modded. you will have to turn the flash head 90 degrees each way to access the tabs. Take your time with this step.
Here is what the flash looks like after it is taken apart. I decided to put the sync port under the battery door on the left side of the flash. Here is a picture of the location of the hole. I just eyeballed it, but the important thing is to make sure there is enough room on the inside of the housing for the jack to fit snugly against the plastic. There are a bunch of little re-enforcement ridges on the inside of the housing, so this step is pretty important. Once the hole is in, there is no second chance.