help changing system voice for only one application

Hi all,
So, on mac, my system voic is alex, that is, the voice that makes announcement and such. When you go to accessibility in system preferences and you go to speech, you will see alex as my system voice. However, I want to use another voice for rs games that is not alex, but each time i want to do this, i have to change the system voice manually. For rs games, i want to use for example, fred's voice for rs games, but is there a way that every time i launch rs games, the system voice changes to fred, and then it reverts back to alex? is there a way of doing this? i tried activities, but it didn't work. Please help.