Here's how I did it.
First, you need to pull your undertail, brake light, turnsignals, plate light, license plate mount, etc...
Keep the hardware, you'll need it later.
Then, you need to make a bracket like this...
Its just a piece of 1/16" aluminum, 90 degree angle, with 1" legs. Drill holes to match the light and the threaded holes on the end of the subframe.
It bolts up here...
The wiring works just like a regular integrated tail, but you have to remove the connector off of your old tail light because the one for the 675 is different...
Now, you need to take your old undertail plastic and trace the outline onto a sheet of aluminum, don't forget to mark the bolt holes. Now cut it out with a set of tin snips and test fit it a few times, then drill your holes. You'll have to trim the end off to allow for the light. How tricky you get here is up to you, you can see a few small gaps in mine because I decided not to mess with leaving little "tabs" to hide them.
The plate I have on now is pretty simple, just a flat plate cut to fit around the tail. I may eventually make one out of fiberglass that slopes into the back of the light so there isn't a step, but it works fine as is...
And yes, its dirty as hell in the pic, the paint really does cover everything.
Paint undertail appropriate color and attach some kind of plate light (to keep the po-po's happy). I'm gonna move mine so its not dead smack in the middle, but like I said, this is the first time I did this, and won't be the final version.
If you made it this far, just make the plate hanger too, its a copy of one on bikebandit, posted on here in another thread. Its just a piece of 1/8" aluminum sheet bent to the appropriate angle. I did a little extra trimming on mine so there's less to see.
If you're planning on spending 300 bucks on an undertail, this is a pretty easy solution. You get turn signals, tail light, and an undertail for the price of the integrated tail (~$100), and the sheet metal and angle (<$20), a plate light (~$15), plus a little time.
Any questions?