Creating graph with two axes, plus shaded region

Hello,

I'd like to create a daily graph that compares two factors (F1 and F2), with F1 on the primary axis and F2 on the secondary axis. There's a third factor I'd like to include as well, but this factor only has binary values and I only need it to show up as a shaded region on the dates in which the condition is true. I've attached my spreadsheet so you can see what I mean.

What I'd like to have is F1 and F2 on the left and right axis, and then have the shaded regions appear behind them but stretching the full way across the graph (i.e. from the max to min value on the y-axis). I know I can change the "1" values to 2.5 to have the shaded region reach the top of the graph, but I also want it to extend to the bottom of the graph, and I was wondering if there's an easier way to deal with shaded areas.

Any ideas?

Thanks,
R