I just did this with the Ultralight V because a repair patch failed. (The original hole was caused by a small child swinging a four-foot straightedge.) Thankfully, the hole was below the knees.
By my estimation - ask me after the pad has stayed inflated all night - you don't need to remove the insulation where you iron. After all, the manufacturer fused/ironed right through all the interior layers.
Granted, the layer of plastic membrane that accompanies the insulation will melt and squeeze out a little, so I did iron over a piece of newspaper.
I cut it off in a reversed V, just beyond straight, because the sides pull forward as it inflates. It is now more or less straight.