I have a feeling that this feature is controlled by the car's computer.

For these late models (although you neglected to provide specifics of model and year, so I'm guessing that you've got relatively new, used cars), lots of equipment and accessories cannot just be "plugged in" -- their proper operation requires a bit of reprogramming of the car's computer. Similarly, I'll bet that there's a selection on the computer screen that allows the DRLs to be activated, or deactivated.

The questions are, (1) is this so? And if so, (2) will your local dealer be willing to do this (certainly, he won't do it at all without a fee ;-)? While there isn't a federal or state law requiring them, there might be a Volvo official policy.