How do I append to the include path using .rootrc or rootlogon.C?

Ahha!

Taking that and combing it with advice from this post, I put this into my rootlogon.C:

{
	gInterpreter->AddIncludePath("/usr/include/glib-2.0");
	gInterpreter->AddIncludePath("/usr/lib/x86_64-linux-gnu/glib-2.0/include");
}

And there we go.

Thank you!