This project has now been shelved until a later date (we're still going to be using Kibana, just without the onclick customisation, though that is likely to be coming back).
For posterity, and anyone else who needs the information, this is far as I got. I should also add, this relevant to Kibana 4.5 and the histogram plugin.
Specifying custom OnClick handler - overridden by Kibana
In the JavaScript file specifying the parameters for a visualisation (e.g. histogram.js) you may insert the following into the "VislibVisType" initialisation code:
return new VislibVisType({
...
listeners: {
click: function() { alert('clicked!'); }
}
...
});
It appears only a single click handler is supported (I have not tried setting "click" to an array of functions), and that whatever you specify is overridden by "something" in the Kibana code base. The overriding click function pertains to drilling down through the chart data, and as far as I can see, this is standard Kibana functionality.
Specifying OnClick within the Kibana code base (hacky idea, but if you are pressed for time...)
In the Kibana source code (src\ui\public\vislib\visualizations\column_chart.js), within the prototyping for the "addBars" function, it is possible to access a "bars" collection that relates to the bars you see on the visualisation. It is then a trivial matter of adding an OnClick thusly:
bars.each(function() {
$(this).on('click', function () {
alert("clicked!");
});
});
I stress that this is a flagrant disregard for the intended structure of the visualisation wrapper, but lacking any information relating to what I wanted to do, it was the only way I could to achieve the goal.
Should anyone happen upon this post and realise what information is missing, it would be helpful if you could chime in. If only to assist other developers in the future, and myself if I come back to this.