I have a supercharged Cobalt and a 2.4l HHR. I recently discovered that the E67 controller in my HHR has supercharger controls (under Torque Management in the Engine group). Upon further research I found that the E67 is used to control some supercharged applications, most notably the supercharged 4.4L Northstar V-8 with VVT!
So I then compared the pins on the ECM connectors between the 2.4L HHR and Cobalt to the Cadillac STS with the LC3 supercharged Northstar and found enough commonalities to guess at a good connector configuration that could be used with the LSJ. Based on past experience with "creative rewiring", I have a high degree of confidence this would work.
The E67 has several tantalizing advantages over the P12, I think. First, it is a fully modern controller that is faster, and it fully uses GMLAN rather than Class 2 (like the P12). It offers two tables for MAF calibration, allowing higher frequencies to be read than the P12 and better resolution for lower frequencies. The fuel cutoff (if you've ever revved a 2.4L) is far more gentl than the P12's. The E67 has the Cylinder Charge Temperature adjustment features, which can help better approximate the charge air temperature inside the cylinders. The more sophisticated VE and speed density systems can greatly enhance airflow estimation (though tuning it can be a pain).
The only big thing I see missing is that the boost gauge is driven by the P12 controller via a pinout; I cannot see if there is a similar pinout on th E67. And besides that there would be no way to properly set the output voltages corresponding to the charge air boost/vacuum pressures. The gauge on the new Turbo Cobalts and HHRs use an ECM pinout also, but the dial's different scale means different voltages on the output wire for different pressure/vacuum pressures. I once obtained a gauge for the new SS and tried to use it in my supercharged SS, but it did not read the correct values. It was clear that the needle moved to the same physical location as it did on my gauge from the superchaged car.
Here's the thing that is truly interesting: a "hybrid" LSJ engine incorporating VVT. I'll bet you could use the new VVT 2.2L as a basis to do just that. Just consider that the 2.2L engine gained over 10 HP when it went to VVT in efficiency gains (mostly) from using VVT technology. Of course, this introduces the cam offset variables into the VE equasion, turning it from a 2-variable system into a 4-variable system. I have created a Mathcad worksheet that should be able to calculate the correct values for the full equasion (15 coefficients!), but it requires a good amount of log data to perform multivariate polynomial regression with.
I put this out in case anyone here has ever considered this. I have the Excel spreadsheet I created that details the connector pins for the ECU. The VVT idea is a pie-in-the-sky kind of thing; I think it's worth looking at even without a major hardware change like that. But I'm a crazy tech head who enjoys problems like this.
Right now I don't have an extra ECU or the desire yet to rewire my ECU connectors in the engine bay (I'm already working on a big rebuild project), but if anyone out there had the time and the inclination, I'd be happy to lend any information I've gathered on the subject. I submit this for your consideration as an intellectual exercise, but hopefully at some point it will be a real endeavor. Enjoy!