Multiple data sources on one graph, from a template

[riversdev0]

Imagine a situation where you use the standard "Interface Traffic" template that is bundled with Cacti to monitor two interfaces on a Cisco router. Normally this produces two graphs (one per interface index number), with two datapoints per graph (input packets and output packets), where both datapoints are tied to the same interface index. This works great, but imagine a situation where I'd like both of those graphs combined into one, and I want it done by the template and not manually. For example, I have a bunch of routers like this, and I'd like a single graph generated when I add the router to Cacti.

Described in a different way, I'd like to produce a single, combined graph with data from all selected interface indexes.

Is this possible, or is it going to be a manual process? Any guidance would be much appreciated.