New Gadget for SLA Commitment Period based on recent historical Cycle Time

I need a dashboard gadget and I can't figure out how to create it. The style should be similar to 'Greenhopper Days Remaining' - Big Bold Number.

The information it should provide relates to Service Level Agreement commitment projections based on historical data. This concept is especially used with Kanban processes, where a commitment is made as a new task starts, that it will be complete within <statistic> days.

The commitment is based on the (recent) historical mean for the cycle time (ie."work started" - to - "done" period) for issues [of that type] PLUS 2 standard deviations.

The problem I am striking is that JQL seems too primitive to allow me to select an appropriate set of records and perform statistical calculations based on values for certain fields in those records.

What is needed is:
Where Project is <name>
Pick the (configurable number) most recently "Closed" or "Resolved" issues
For these issues, calculate the mean and standard deviation from the time difference between the "work started" and "done" timestamps
Display = Mean + (2 * Sigma)

Of course this would also be best with additional filtering, so the set of issues calculated over would be taken from a selected Component or Version or Assignee. As we are using 'shirt size' estimates via a custom field, it would be good to filter based on that also, so that we can have a gadget that displays the current SLA commitment for each estimation size.

An additional option to display the actual mean would be useful also.

I attach suggested graphic and config mockups