What happens when the airfield elevation is >1000'?
Many modern aircraft have both rad alt bugs and settable minima, so why the need for an altimeter bug? If you stick to the levels published on a procedure, an altimeter bug is useless and arguably a distraction to other markers, such as Alt Set and procedure minima.
If your pilots ignore the calls, I would be heading down the route of training, rather than introducing new equipment, as amendments to company SOP will typically be cheaper and more effective. Put it this way, if pilots are not doing what they are supposed to be doing now, then what is to suggest they will even use a altimeter bug if it was fitted?