If you can get the airlines to program the hold in as part of the STAR in the Dep/Arr page of the FMC, you wouldn't have to worry about guys following the magenta line past the hold.
The aircraft would automatically enter the hold as part of the STAR & the flight crew would manually have to exit the hold when given onwards clearance.
Every aircraft with an FMC should be able to have this programming. The airlines just have to be convinced (a few fines should do the trick) & then instruct their data supplier that this is what they require.