Ok, here is where you can get unlimited soft drink refills, while eating there only:
All Table Service locations
Rancho Del Zocallo
Plaza Inn (They are resisting getting the large cups, but if they do, this is rumored to stop then as well)
Officially Rancho Del Zocalo and Pizza Port have stoped when they started selling large drinks; howver, most cashier will permit it.
White Water Snacks
Tangaroa Terrace
Ralph Brenan's Express Kitchen
La Brea Bakery Express (but who know when they reopen)
Tortilla Joe's Cantina
And pure speculation, but based upon experience:
Earl of Sandwhich
In all honesty, I think they should offer $0.99 refills on souvenir sippers.