Well the dealer wasn't any help. I ask the guy at the desk for the plugs, then he proceeds to the computer and asks me what car I have in an effort to find the parts numbers for it. He then tells me that Volvo would not sell such a thing since they are concerned about safety and would not want you to take your front plate off.
I just got back from Pep Boys (a general auto parts store in case you don't have that particular one in your area) and I picked up a little box of Splash Sheild Retainers for GM vehicles. They look identical to regular bumper plugs and have a 3/8" fitting, the same as the holes the dealer drilled. I tried to put them on, but its a really tight fit. I'll have to push really hard to get them in, potentially damaging my bumper, so I'll just sand them down until they fit nicely. Part # 45510, about $1.80 with tax for a pack of two in case anyone is interested.