Custom positioning of bars in a bar-chart

I want to use highcharts to generate a bar-chart, in which the bars are annotated with images. To make this look nice, I want the gaps between the bars to be uneven. How can I achieve this?

This is the sort of effect I want:

bar chart with gaps http://www.cs.ucl.ac.uk/staff/d.wischik/Leftovers/bar-gap.png

I will place the images manually, in Javascript. In my application, the heights & areas of the images are meaningful (they're not just the flowers I'm using here for illustration), and so I want to be able to control the gaps betwe开发者_开发问答en bars.