How to switch the sidebars?

If I use three-column layout on the front page (two sidebars) and only one sidebar on posts and pages, the “primary sidebar” appears on the left on the front page but switches to the right on posts/pages. Is there a way to make the “primary sidebar” the one on the left instead to avoid this?

I have tried the custom sidebars plugin recommended and this is a solution, but it seems overkill for what I need and the plugin has its own issue, which I have just posted about on their support thread. Assigning the right sidebar as primary, if possible, would avoid all this.

Many thanks.