I have already answered the question in your support ticket, so I am posting the answer here as it might be useful to other clients.
The described configuration is not currently supported in RadHtmlChart, but you can achieve a similar appearance by using the "gap" property of the series on the client-side like this:
//get the chart
chart = $find(
"<%= Chart.ClientID %>"
//set the "gap" property of the first series, i.e. the ColumnSeries in our case
chart._chartObject.options.series.gap = 50;
//repaint the chart to apply the changes
You can specify whatever "gap" value you want. I also attach a sample page, so you can test my suggestion on your own.
You can also vote for this functionality in our Feedback portal
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to the blog feed