If the keyboard has carbon coated rubber contacts, you can recoat them with the Circuit Works CW2605 keypad repair kit:
http://www.newark.com/product-detail...log/29687.html
I've used that stuff many times, it works great.
If it has the brass ring contacts, you could take them off of 2 of the function keys that are never used. The enter key, just like the space bar, often has 2 contacts.
Lets see some pictures, if you can.