"forcing" a layout within PHP

I have a custom page template called template-books.php. I can create a page in wordpress and assign this template to it. I also set the layout to just have a left sidebar. This is all good.

Im using a tag cloud widget in the left sidebar to allow the user to filter the list of books by tags. This is also good.

Where things fall over a bit is when someone clicks on one of the tags which subsequently loads up my taxonomy-book_categories.php file. The results are perfect but for the fact that I loose my left sidebar. I get the right sidebar just fine because the right sidebar is the default sidebar.

Yes I could set the default sidebar to be the left one but then I’d have to go through all my pages and set the layout on them to use the right sidebar or no sidebars as appropriate but that’s a bit of work.

What I’d like to do is to enforce the use of the left sidebar in my taxonomy-book_categories.php file. Does anyone know how best to do something like this?

Thanks
Chuck