Drop button on Call Master

[Definity]

Is there a way to have a drop button (or kind functionality) on Call master. Our agents does a conference on call masters & for some cases they need to drop the last dialed number from conference...603E1 doesn't allow to do assign drop button on any key.

Is it possible somehow.

 

[4merAvaya]

CallMaster III (603E1) have a 'drop' button in the upper left-hand corner.

Kevin

 

[Definity]

We use Call master IV & CM4 doesn't have the drop button.