You can tween values mate, so you could in essence transition the global pause value between animation frames from current value to a high value over x time. Another thing you could do is insert a script into the final frame of each arc of the animation to increase current global pause value between frames by let's say 10 each time the frame is hit whereas clicking on the left or right areas you specified will reduce delay value by x amount down to a min of 16ms as that's the fastest you can go (60fps).
I'm not sure about without using Lua script. Anyway, to adjust pause value...
local pause = Animations["example"].AnimationPause
if pause > 16 then pause = pause - 10 end
if pause < 16 then pause = 16 end
That example would be for reducing the pause value to make the animation faster.
For slowing it down would be a bit more complicated as you would need to make it stop entirely, so you might want to force it to play a single specific frame once the speed gets to a certain delay value.
*edit: thinking about it, there's something else you could do. If you created the animations as static images & assigned the same value to each one, you could use the value tween action part Simon added & transition through the values. That way it will update frames over x time. I don't know if it will look very smooth, but with a few if queries you should be able to create a fully non-Lua script method for it.