You could probably use instant decaf flakes and make something similar.

I've been pretty boring with my shakes, mostly all chocolate. Sometimes I add DaVinci B52 syrup, have also tried almond extract. I made one with plain protein powder that I added some vanilla too as well as DaVinci cinnamon syrup and a dash of cinnamon. I have DaVinci eggnog syrup too and keep meaning to try that one. I have a bunch of blackberries from my garden that are in my freezer, and keep thinking I'll toss 3-4 of those into a shake with maybe some orange extract. I did buy some diet black cherry soda (sweetened with sucralose) and mixed it with a chocolate shake to try to Black Forest Cake recipe in the book, but it was too sickeningly sweet for me.

So that was a revelation. I have not had diet soda in about 6-7 months, and I was suprised at how my taste buds had changed. Just the plain soda alone almost made me gag.