What do you want to do that you can't do with the rules as written?
"As you walk up the road Sweathog yells "take 'em!" and the guys on the rooftops to either side here start opening up with their Uzis. Fishstick, what do you do?"
"Crap! Is there anywhere I can take cover?"
"Yeah, there's a little kind of low shack where someone's been living, like a hobo in a box but made of sheets of corrugated steel, just beside you, but it looks pretty seriously rusted out. You can duck behind it, or there's a concrete jersey barrier up ahead that looks sturdier, you could try getting to that but you're going to get shot at."
"I run for the jersey barrier. Acting under fire?"
"Yeah"
"That's a 7."
"Okay, you take 2-harm but you're now under pretty solid cover. June?"
"I'm diving back behind the rusted-out shack."
"They spray some fire at it. You don't get hit directly but little rusty scraps are splintering off and spalling. Take 0-harm, but make the harm roll."
"5, I'm okay?"
"Yeah, a little rattled but you can act."
"I yell 'Sweathog, you've got two choices! You can put the guns down and we can talk, or, well, Fishstick brought the grenade launcher!' That's a manipulate, and I get... whoops, a 5."
"Sweathog yells back 'Grenade launcher! Great idea!' A second later, bam, it feels like you both got hit with god's own sledgehammer. The jersey barrier is cracked in half, Fishstick, you're no longer under cover, and you take 4-harm and you're stunned. June, you're going to have to act under fire to avoid getting pinned under the shack as it collapses..."