I've been trying to figure this out too. So far, I've seen a couple of basic approaches, both require a double offset (if you will) to establish the tang shoulders. If you have good hammer control, you can do it by simply hanging the blade over the anvil and offsetting the tang with hammer blows. If you're like me, and keep hitting in different spots with each blow, than some sort of fullering approach works better. Thus, something like the device Raymond uses.
You put your blade in between the two fullers (in this case they're rigged up using a bolt as a pivot point) and whack away. You can get much cleaner shoulder indents (well, for us wayward hammerers, that is). There are various ways to rig up the fullers, such as this pivoting one. The sliding guillotine, or blacksmith's helper, is another, as is the more traditional spring fuller.
Once you have the offset shoulders established than it's just a matter of drawing out the tang with basic blacksmithing use of hammer and anvil.
