Flameout hop additions are pretty common...quite a few of my haus recipes have them.
When you turn off the heat, the temperature doesn't immediately substanitally drop so you still have wort hot enough to isomerize the hops, yet not enough to drive of the volatile aroma oils. So you'll get some definite aroma/flavor benefits from this.....(look at some of the info on here on continuous hopping, or the late hopping methods some people are using where all the hops are added at the end of the boil. Usually starting in the last 20 minutes for an explanation.)
Basically what will happen is you get a nice hit of aroma flavor but the esters don't get driven off at the boil.....
Just drop them in and fire away with your chiller, you'll still get all the benefits while it is pumping through your chiller...OR you could drop them in a minute before flame out.
BUT, I think you are right, in that it is sort of the same thing, in your setup, as using a hopback, except with a hopback you are in effect filtering the wort through the hops, so you won't get hop gunk from it in the "finished" product.....you could use some chore boy stainless scrubby in front of whatever is on the inside of your spigot to filter the hop gunk.
I think Yuri or Orfey has a pic of their setup where they have a dip tube in the kettle side of their spigot and use a little ball of choreboy as a filter.....