Flippant:frivolously disrespectful, shallow, or lacking in seriousness

I think it is flippant. he's calling the people flippant. Think of it as a "you understood" sentence from back in grammar school. If I said, "Carry this box", you automatically know I'm referring to you.

"Ignorant flippants in the congregation" - It's understood that the people are being flippant. Maynard is just using a little poetic license. While not gramatically correct, the message is conveyed.

Ignorant flippants in the congregation
Gathered 'round spewing sympathy, spare me.

It actually fits perfectly there, meaning that the people at the wake weren't truly sorry. They were just sorry because they were at the wake.