[dsraven]

bolt the flat edge to a 2x4 to keep that edge from getting bent inadvertently. then lay that edge on the floor on top of another 2x4 or maybe a 4x4 post, something good and strong but straight. that will keep the straight bottom edge straight but also just up off the floor. lay the rounded top edge on another 2x4 or a 4x4 post so the top and bottom are both the same distance off the floor and not able to bent the opposite way too far ()lay it down so the bulge is pointing to the sky). then, using another long not easily bent item like another 4x4 post laid across parallel to the other posts, start working your way across the bent part. you could lay some stoppers on the floor so whatever you do the panel can't get over bent. imagine reverse engineering. start at the least bent spot and work towards the most bent spot. by the time you get to the worst bent spot it will likely be less bent and the steel won't be all stretched outta shape from whacking an already stretched part. the long helper 4x4 post will spread the weight of whatever you use to push with, be it body weight, a jack or a bug hammer.
the irony would be using the same item(4x4 post)that made the bend to help get the bend out. using a hammer without something between it and the panel may result in more, isolated, damage unless you have done this before and understand how it works.
just my "use what you got" mentality.