maybe 7-10 seconds of fuel in the lines before the engines flame out
And that's just one of the problems. The NTSB Reporter is a good source of reports on what happens when pilots without aerobatic training and in non-aerobatic aircraft have a go at rolls and loops. Spoiler: it usually ends badly. I'm sure there are pilots that could successfully roll a 737 inverted, potter along for a while (without power), then roll back upright without the slightest fuss. Just not many. (A bit like the Virgin pilot who landed a 340 at LHR a while back with one main gear non-deployed. Turned out he was also the current UK aerobatic champion!)
The first part of an aileron roll in anything (even an Extra with its 400 degree/second roll rate) is to pull the nose up 30 degrees or more - 45 degrees in a Citabria. If you don't, you will finish the manouevre with the nose pointing pretty much straight down. No idea what a 737's roll rate is, but probably not very high. My aerobatics instructor explained to me once how you decide whether it's safe to roll a non-aerobatic type (he says C130s roll very nicely) and it's not just a case of bang over the stick and wait, far from it.
Not to mention the total pandemonium in the cabin. OK, it's better than dying. But still.