Add second sidebar, to LEFT of main column

Forgive me for asking here, but I want to modify Laila 2.1.

I just want to add a second sidebar, but since I want it to the left, centering the main column, it’s not as straightforward as I thought. Main column is also fixed-width, and I have no idea what the implications are if I just plunk a third column into the page. I also don’t know if the widget-readiness of the existing sidebar would automatically apply to the new one.

Is there an easy answer for this? Adding the code for the third column seems easy, but that doesn’t address the left-side location nor the width thing.

Thanks.