If I were you I would simply swiitch over to the Aluminum Upgrade wheels that came on this vehicle in the higher optioned state. There are nothing but advantages to doing so. You may even find a set with good tires already mounted on them at an alarmingly LOW price… People sell stock aluminum wheels from this model all the time. You may be quite surprised at how affordable they can be.
Aside from a wheel upgrade I would look at your current caps… look around the outer rim… You may have missing tabs and or a missing steel “Spring Ring” that all make the hubcap able to stay firmly placed on the wheel. In fact those caps should really not come off very easily…so there is more than likely something wrong with those hubcaps.
If I was going to use Zip Ties to secure the caps I wouldnt simply go around the outside like in the picture,… You can do it in a more clandestine manner…