convert side box to centre box option

Are there any plugins that give a store owner or customer the option of forcing a side box to display instead as a centre box?

Other than using responsive css media to automatically do this on small screens, any suggestions how this might best be achieved.

Thanks

You'll have to build your own centerbox that does what you want. The instructions vary based on the template you're using - look at how your template builds centerboxes and go from there.