Bob, I know that you are probably looking for something easy and very produce-able, but think about this:

In these turbines the fuel tubes point into the sides of the fuel sticks (tubes) in such a way as to spray fuel into the tube's ID. The tube is glowing red hot when the turbine is running and therefore vaporizes the fuel upon contact. That allows a very well mixed air/fuel mix to enter the primary combustion zone.

Perhaps a similar strategy would work here. I would make as small a hole as you can in whatever tubing-end you use. This could be set in a recessed fitting that is welded into the tailpipe's wall. The spray is pointed at a button/tab/piece of stainless/Inconel that is exposed to/flush with the flow in the exhaust. This button/tab/piece is glowing VERY hot, due to the flow just aft of the turbine wheel. Your injected flow would vaporize immediately and mix well. As it exits the nozzle, into O2 rich ambient air.... VIOLA! Desired effect occurs!!! You could mount two or three of these equally spaced around the circumference.