Animate to state?

Hey crew!

I've got a thin line at the bottom of each slide to track the user's progress. I have it set up with 12 states, 12 different lengths. It grows to the next state (length) as the user progresses. I used a "wipe" animation to make it grow from the left.

But here's the minor problem. Each slide, it starts at zero and then wipes to full length. What I'd like to have it do is start at the previous slide's length and then only animate the 1/12 of the way that'll bring it to the current slide's length. Is there any way to make a shape not animate into its starting state, but then animate into another state?

The Animate menu is greyed out when editing states, so I'm guessing it's something intentionally left out, but wanted to check with you geniuses before I gave up.