1 dock connector from Kineteka
2 10k ohm resistors - needs to be 20k, a single 22k is too much
1 donor USB extender cable
Various heat shrink, tape, etc to taste
Pinout here. With the connector plugged into the Tab, and the Tab oriented with the chat camera on top and the connector on bottom, pin 1 is to the left of the connector.
Chop off the plug end of the extender, separate out the wires, cut / strip / tin. Cut off the shield. Slide on the plastic shroud for the dock plug and a piece of heat shrink for strain relief. Don't forget this or you'll have to undo the whole thing (like I did). You might also want to cut thin heat shrink to go around each wire to protect it from shorting at the connector pins.
Solder the two resistors in series and put them between pins 13 and 15. This tells the Tab to go into OTG host mode. Be creative. Surface mount parts might be better here.
ground (black) to pin 1
green (D+) to pin 3
white (D-) to pin 4
red (+5V) to pin 6
Test this out before shrinking the pins by plugging into the Tab along with a USB key. If it works, you should get the message above.
Once it works, put the connector shield, spring clip, and shroud on.
All said and done, this comes out to about half the price of the Samsung adapter, but at the expense of some elbow grease and potential unreliability. I expect clones will be showing up on eBay someday though, so if I've done anything useful here it's to entice our friends in China to start their assembly lines.