Out of the box, report parameter printing is already supported automatically. However, if you want to support a re-rendering from the preview window, you need to signal your support to List & Label by setting some additional options. For convenience, this feature uses the same callback as drilldown printing, so in most cases you can simply reuse your existing code and just make sure it works even if no drilldown filter is set in the passed structure (i.e. all table IDs and key field values are empty).