They could draw material from several issues of the War Journal, War Zone and the MAX Series. There is a nice scene, I think it's in the first issue of Volume 4 where the Punisher saves a woman from a thief, but he is really more interested in beating up the guy than save the girl...
Woman: "Y-you're the Punisher, right? You go around killin' criminals? Thanks man...!
Punisher: "For what?"
Woman: "For - for saving my life!"
Punisher: "Right."
There could be a similar scene near the beginning of the movie, to show that something strange is going on inside Castle. Another nice exchange between the Punisher and a woman, I don't know what issue...
Woman: "But - I mean - slaughtering criminals isn't going to change what happened to you! Surely you can see that all this violence is nothing but a pointless, ever-escalating spiral of negative energy?"
Punisher: "No."
Woman: "Well have you ever considered stopping for a while, just to give it some thought?"
Punisher: "No."
Woman: "What's in the backpack?"
Punisher: "Flamethrower."
Woman: "You're kidding, right?"
Punisher: "No."