gauge swap

I have a friend with a 99 GMC sonoma and he wants to change the gauges on it but heres the problem. The dealer that he took it to to input the data for the other gauge contacted GM to get the authorization number to change the options list but GM says they're no longer allowing option changes (procedure requires the tech 2 to download the data from GM to allow the options to be changed in the ecm) how ever he contacted some one that said if he buys a new gauge that the info on it should be blank and the dealer should be able to download the proper data to ecu, however Gm says that if the truck didnt come factory with that option then it wont work. I'm sure that there is some procedure to bypass this becuase they also say you cant add another radio that didnt come stock on the truck but he bought a new cd player that was blank and went through the learning procedure and it works (cd player was an option in that truck but this one didnt have that option on it). Has any one else came across this problem or know any way to allow the gauge to work?
Some info on the truck : auto, vortech v6, no tach in the instrument cluster and he wants the tach there, manual windows and I belive the locks are also manual.
The gauge works to a point when its installed it just doesnt show the fuel level, oil pressure, or the miles. From what we have found the data stream has to look at the fuel and oil gauge to see if its the correct gauge and it also checks the fuel gauge when the door opens during certain operation modes.
Any help, info or good guesses would be great becuase short of reverse enginering the program that allows acces to the options list we're both at a lose of ideas.