try sending hoverdata on double click:

etpinard · etpinard · commit 9c19406d25df · 2016-02-17T11:25:42.000-05:00
- double click on a data pt now (1) fires a click event,
  (2) fires a double click event and (3) fires another click event,
  with the same event data
- double clicking not on a data pt fires a double click event
  with null event data
diff --git a/src/plots/cartesian/graph_interact.js b/src/plots/cartesian/graph_interact.js
@@ -1821,7 +1821,8 @@ function dragBox(gd, plotinfo, x, y, w, h, ns, ew) {
             }
         }
 
-        gd.emit('plotly_doubleclick', null);
+        var dblClickData = gd._hoverdata ? {points: gd._hoverdata} : null;
+        gd.emit('plotly_doubleclick', dblClickData);
         Plotly.relayout(gd, attrs);
     }
 

Original file line number	Diff line number	Diff line change
`@@ -1821,7 +1821,8 @@ function dragBox(gd, plotinfo, x, y, w, h, ns, ew) {`
`1821`	`1821`	`}`
`1822`	`1822`	`}`
`1823`	`1823`
`1824`		`- gd.emit('plotly_doubleclick', null);`
	`1824`	`+ var dblClickData = gd._hoverdata ? {points: gd._hoverdata} : null;`
	`1825`	`+ gd.emit('plotly_doubleclick', dblClickData);`
`1825`	`1826`	`Plotly.relayout(gd, attrs);`
`1826`	`1827`	`}`
`1827`	`1828`