CrunchBite!!!
You know, from Red Vs. Blue? The one that goes "Blarg, blarg blarg, honk honk blarg"
Bring the dinosaurs that everyone loves into ODST, they hate the covenant too now, so it could make sense to see them shooting grunts and brutes. Just make up a bootleg story of how there was a lone elite, CrunchBite, trapped on a Covenant ship, and just happend to escape.
Blarg?