Graphing sum of functions or data sources

I have a simple function called pppoe()…

oid("iso.org.dod.internet.private.enterprises.cisco.ciscoMgmt.ciscoAAASessionMIB.casnMIBObjects.casnActive.casnActiveTableEntries.0")

I’m trying to graph total PPPoE active connections across all of my PPPoE concentrators in the dude. Can I do this on a single chart, either by adding data sources, or by passing different devices through the function and getting the sum?

EX:

in the new data source i’d select no device and in the code field i’d put something like this:

pppoe(P1) + pppoe(P2) + pppoe(P3) + pppoe(P...)

P1/2/3 being the device name of the snmp OID I’d like to retrieve. Is this possible? Or is there another way to graph the sum of data sources?