Go back there and show them the manual. If they say they don't know how to do it, talk to the service manager and ask him/her to find out. They are able to change that, along with several other settings(seat belt chime, DRL, etc) with their TechStream unit. Most of the time they are too lazy to do it. Just a FYI, they will charge you half an hr, possibly an hr in labor to do this if they "figure out" how to do it. Not sure if it is worth it to you.
As for DIY, I dont think there is a way.