For someone without the mechanized tools for metalshaping, much can be done still with simple hand tools to limit the damage done to the panel. For adding stretch, pounding sporadically into a sand bag will quickly add "walnuts" to the panel, where a less aggressive method of methodical, precisely located overlapping strikes will limit the size of the walnuts, and more importantly the DAMAGE we need to fix. As with most anything we accomplish in our restorations, match your efforts to the tools within our disposal. If you don't have a planishing hammer, don't beat the panel to death that it can't be completed without one.