What I ended up doing is use the same idea in the tutorial along with Spriter (the free version) to create a 101 frame animation, with its speed set to 0.
Frame 0 is the radial when it's empty, and frame 100 is the radial when it's full. Thus, I can just take the percentage of whatever I'm keeping track of and every tick set the frame of the radial animation to that percentage. So 50% would be frame 50, 75 percent would be frame 75, etc.