Matt -
I've had the exact same ones. Unless all the roads you travel are smotth as silk, they will pop off. It's just a matter of time. They will also get damaged in a car wash that grabs the tire and pulls it along (happened to me). This is because they bow outward. The also puts them at risk when you parallel park at curbs.
You could just get a set of run-of-the-mill hubcaps that are mostly covered and "fill in the blanks" :
Hubcap Haven: Aftermarket Hubcaps 15 Inch 52s Silver Set - $50
Idea that may not work: I don't like drilling into the steel wheels, especially when the tire is still on the wheel. You know those center caps that screw onto the lug bolts of your wheel? They usually come with custom wheels. Start with one of those. Drill a hole in the center of it. Drill a hole in the center of the racing disk. Push a bolt out through the center of the center cap and "cap" it with a cap nut ("acorn" nut). You would have a little "center bump" on the center of the racing disk, but it might keep the disk from flying off. I am guessing, however, that the disk will distort when it "almost pops off".
CarloSW2