Generating a connected graph instead of disjoint method graphs?

Is there a way to generate a single connected graph for a codebase like Joern's export.graphml, instead or in addition to the disjoint graphs that are currently generated by Atom for each method?

Alternatively, if that is not supported by Atom --export... can you recommend an approach to post-process the generated disjoint graphs and reconnect them once they're loaded in networkx for example? I already understand how to connect nodes in networkx, but I'm not really sure which source nodes should be matched with which target nodes in the CPG, and what attributes on these nodes should be used to match them.

Thanks!