I am dairy free now, so it has been a long time since I have had a mocha. I am sure this tastes nothing like SB or McD's, but here is what I do:
A while back, I started freezing my leftover coffee in ice cube trays. I felt so bad throwing it out. I mix it with my creamer sometimes, then freeze.
Each morning, I make one press-full of coffee. I drink a large mug in the morning and leave the rest in the press.
When I need my 4 pm pick me up, I pour some chocolate soy milk in a glass along with the coffee in the press. I add a smidge of simple syrup that I keep in the refrigerator. Then, I add my frozen coffee ice cubes. The ice cubes keep the drink from being watery. I
this, it is as close to a mocha as I have been able to get, since I don't use an espresso maker and can't have dairy.