I am not sure if all Starbucks outlet do this. But it won't hurt to try, right? Because in my place, whenever we order frappuccino with jelly, we ask the staff to place the jelly in a separate cup.
That way, I can have more frap in my drink and also get more jelly since they fill up the other cup where the jelly will be placed.
As a result, I get more. Jelly overload!