I would go for a service contract. Depending on how complicated you wanted to get, you could have the dragon demand the PC's accept a quest/geas spell for each egg they wish to obtain.
I'd probably make the first one particularly sadistic, so the players must decide how much they want the eggs, and really build up their dread. Perhaps, obtaining a young fair maiden from the neigboring kingdom as a sacrifice to the dragon, assasinating a powerful member of court in a neigboring kingdom, assasinating a powerful figure in the dragon cult (publicly).
If I knew that the PC's needed all four eggs, and three eggs would be a good as none, I might get overly clever. As the PC's present themselves to recieve their quest and egg, the first would be commanded to follow the dragons instructions to the best of the characters ability until the next sunrise. The second might be ordered to commit some heinous act that might actually serve the ends of the dragon, or just serve as entertainment.
The third would get off the easiest. But first the dragon would command the fourth to come foreward and bid him kneel behind the third. Then order the first to come foreward, draw his blade, and kill the fourth if he made any attempt to resist, and then turn on his remaining friends. The player of course has his choice, but the penalties are quite stiff. And there's a dragon there anyway.
The third would be compelled to tell the dragon everything the party planned to do with the eggs, who needed them, where they were, and why in exahustive detail, omitting nothing.
The fourth, oh the hapless fourth. He'll learn why it's sometimes better to be first. His mission will be to betray those who wish to use the eggs in the most cruel vile way a super intelligent and devious dragon can concieve while destroying the eggs.
The first would obtain an item of inescapeable detection that would be all but impossible to remove, and make it a trivial task for the dragon to scry on them for his amusement. Something like pushing the item into the first pc's body under the ribs and then having him quaff a nice healing potion or apply a soothing balm comes to mind. Yeah, after the next sunrise they can safely try to take it out, but would you really let your buddies perform home surgery on you in the woods sans anethstetic?
Even if the red dragon doesn't end up as a reoccuring villian, you can rest assured than when the PC's get buff enough, they'll make time to settle that score. And best of all, they'll make all kinds of enemies (pc number 2 assasinates the good king, powerful general, etc), pc number 4's betrayal will certainly leave a bad taste in the mouth of some, possibly rivals. Ready made adventures.