Single save button for a compound plot?

I have a server app that is a layout of two plots and some controls. I would like the option to save the state of the (entire) app as a png file. So far all I have been able to figure out is to attach a save tool to each of the two plots and save them separately.

Is there a way to attach a save tool to a collection of plots and save the group of them all at once?

The SaveTool can only save one HTML canvas (i.e. one plot) at a time. The only way to save an entire layout with multiple plots is to use export_png function. Since this is a Python function, it can only be used within a Bokeh server application.