The last cook that I did on my Bandera, I also tried using the "minion method". The lid to my firebox is not very tight, and the dampers are difficult to control. While it did much better than when I was just burning logs as far as fuel consumption is concerned, it was far from efficient. I am thinking of securing a new firebox lid, sealing the entire damper end, seal the lid with some nomex gasket material, and get a bulkhead adapter that will allow me to use my guru. I am curious to see how the fuel consumption goes with that config.
One other thing that you could try, is to enclose your basket with firebrick to cut down on the combustion air, as long as air is available from the underside. I find that this technique works very well in my WSM when I am going for the 225-250 range. Can't get much higher than that with the firebricks. Just a thought.