The short answer is "nope".
The long answer is...they sell "souvenir" mugs. Those come with one free drink (cocoa, coffee, that sort of thing) when you buy them. After that, you might be able to have a drink put into it, but you are going to pay full price for that drink. And if a CM is filling that drink order, they are very likely NOT going to put it in the mug, because of various reasons (sanitary, they aren't sure it's the same ounces (it is, at least for the coffee to-go cups), etc).
I was getting myself and hubby coffees at WWS once, and I'd already bought a souvenir mug. I first poured coffee into the to-go cup, then poured it into my mug, to see if they were the same ounces.

Then I filled hubby's cup again. The CM made sure to tell me that I was not getting a discount even though I was re-using my souvenir mug.
Aren't you glad I told you the short answer first?
