Disable Hold ? Need solution

I have an inbound call center and they abuse the hold feature by keeping callers on hold forever when not warranted. I have decided to make them park calls instead so the call can time out and go elsewhere. I am trying to discover if it is possible to disable hold on the phones (GXP2160 and S500) or to do it some other way. Ive looked at the config basefiles for both and can’t come up with any ideas. Any help appreciated.

So for the s500 you can control the horizonal soft keys in EPM but the hard coded hold button can not be disabled at this time. We are adding in the next firmware ability to disable the menu button at a request of a user so open a feature request for the hold button and we can get a config option for that.