I'm passive agressive and usually say to them as they turn their back to walk away 'are you going to push your bags through?'. Usually gets them to turn around and push them.

On a side note, has anyone ever leapfrogged someone who is parked at the tail of the line near the bins and slowly unpacking? Once or twice I've grabbed a bin and jumped in front of them since I usually have everything in hand to throw into a bin.