Best way to aggregate multiple series?

I know that SingeStat panels only support a single series, and I understand the reasons behind it, but I do occasionally have the need to add up some queries. Is there native way of doing this? Or perhaps a well-known plugin that supports it? The closest I’ve gotten is using the Table panel set to “Time series aggregations”. That gets me the individual series’ sums in one spot, and so I’d just need to be able to sum up the values in the column.

I’m prepared to fork the single stat panel if I need to, but this seems like a simple/common enough thing that I’m wondering if someone else has already done what I need.