This is going to sound stupid, because I'm sure you've already tried it....but here it goes anyway:
If you have not already tried this, get a few flat blade screwdrivers of different sizes. Sometimes, a little grease on the tip helps.
Wedge 'em (usually one at a time, unless you have four arms) in the spot between the cowl and the bolt head meet (I don't believe these call
for a washer, but if there's a washer, wedge the flat of the screwdriver under the washer and still next to the cowl metal), but not hard enough
to completely screw up the cowl.
As you pry out, just hard enough to get some stress on the bolt/body screw, with your 1/2' open end, slowly go "lefty-loosey".
Another possibility is using a set of Vice Grips and lefty-loosey while pulling back like you are pulling a tooth.
If it doesn't work, then no harm, no foul. Personally, I'd use a Dremel on something like that if nothing else worked.
Remember, though, if you cut it off, you'll have the pointy part of the screw/bolt rattling around in your air pocket...
Probably no biggie. But something to think about.
When it's out, there are a ton of good and ghetto fixes available to you.