Question about installing a WS13A switch

[AndrewFH]

I am installing a WS13A wall switch in my kitchen to control the florescent light. The switch I am replacing is in a gang box with two other switches and only has two black wires (hot and load) and a bare copper (ground). The box does have a white (neutral) wire in the box which I can use for the WS13A. I understand that I will need to use the neutral wire and how to wire it up. The only question I have is regarding the ground wire that is currently connected to the old switch. When I install the WS13A, what do I do with this wire? Can I just connect it to the ground post on one of the other two switches in the box? I saw one post where the poster said they use to just attach it to the metal gang box to ground it, but my gang box is plastic. Any one have any suggestions?
Thanks.

[Mellowmark]

Hook it to any and all metal if possible.  If there is no way to do that then just push it in the back of the box out of the way..