In the duramax world (I just traded my dmax for a 2010 laramie 6.7) we had something called a finger stick that would trick the computer into thinking that the EGR system was still working. We would use a blocker plate and install this electronic finger stick and it would never set a code.
I think the computer knows that the EGR is working by seeing a reduction in flow on the MAF. (I am assuming the cummins has a MAF). I would assume the flow on the MAF is compared to a table in the ECU and the difference between measured flow and the flow indicated on a VE table would be seen as EGR flow.
The finger stick had 5 wires.
MAF signal IN
MAF modified signal OUT
EGR Motor signal IN
The EGR motor looks to be the same between the duramax and the cummins so I am hoping something similar is possible.
I would assume (im no EE, only a lowly computer programmer) that this finger stick would take a position signal from the EGR motor and use that signal to scale the signal from the MAF so the measured airflow through the MAF increases/decreases as the EGR motor opens and closes.
It may even be possible to use one of these finger sticks from a duramax but we would need some electrical engineer type to compare the MAF signals between the two engines and possibly compare the the EGR motor signal so we can determine if the scaling would be correct.
Fingerstick instructions if anyone is interested.
It would be awesome if a similar device could be created for the cummins. If so we could block the cooler off at the manifold and leave the hardware in place, the blocking would be completly invisible to emissions techs and dealers.