If you have a million users that's 100 pissed off people.

My advice:

Publicly expound on how you don't care about those users and they are SOL because they are in the minority. It won't matter because it doesn't affect the rest of your userbase, right?

</sarcasm>

When working on a packet analysis system for a VoIP company, I found that around 1% of incoming UDP traffic was fragmented, the size being around 576 bytes.

I don't know how representative that was (10s of thousands of users, but large users generating more traffic than smaller ones), but < 0.01% is probably on the low side.