Oh boy. Lots of scenarios. 
Ok, let's see.
Well, Wrath's swords were shown to actually break after connecting with Greed's Ultimate Shield. So, I don't really see how the manhandling would work.
Greed's mouth does open. But I looked at the inside of his mouth, and there is Ultimate Shield inside his mouth too. So explosives would not work. Although, I give you lots of credit. That is a pretty good solution to defeat Greed. Can't hurt him from the outside, then hurt him from the inside. Too bad the inside of his mouth is protected.
Well, they do mention numerous times that Greed's shield is the hardest substance available. Wrath even says that Greed has the impenetrable Ultimate Shield. A sword made of diamond wouldn't work for that reason.
I say no running away because I don't want any cheap answers. Just like with Greed vs Lust. People actually answered that they wouldn't fight because Greed does not fight women. And also, you could answer any fight with a running away solution. Too easy and boring. Greed wants Wrath dead in that moment. Wrath wants Greed dead in that moment too.
I don't really need any specific rules. Just each homunculus at their absolute best and no running away.
Well, at that moment, Greed dumbly didn't have the Ultimate Shield on fully. I am sure that Pride's teeth would break if he tried to eat Fully Armored Greed.