Ambush Bug (Irwin Schwab) started as a minor character in the Superman comics. Hes something of a loser and a very scrawny man who has the power of teleportation via a green bodysuit that has been imbued with said power through exposure to interstellar radiation. Ambush Bug has grown from a throwaway supporting character to an everyman anti-hero with a fairly substantial cult following and is popular enough to have warranted several of his own miniseries. He is still mainly used as comic relief, however. How could he cameo humorously? As a generally humorously presented character with the power of teleportation, it would make for a lovely light-hearted little easter egg for Ambush Bug to teleport in to the background - even if it was just for a couple of frames - to make his cult following go wild. He has links with Superman and the Justice League, so having this occur in either of those movies would be a nice cameo to raise a smile or a giggle.