Inserting manual Threshold line in Performance Graphs

When creating dashboards showing performance graphs, is it possible to manually put in a threshold line on the graph?

I’m using version 3.

Not in version 3, though in v4, the SQL tile has a line graph option, and you can place trendlines etc. on there within the query itself.

Upgrading to v4 would be the first step, but a feature request would also be a good idea.