Ah, this sounds like a fun question. Well, you could go the easy route and change Mercutio's name to Mark Q. Tio. Mercutio is such a slick talker, though, that it would be nice to give him a name that reflected his eloquence. Perhaps a name like Mark Quicksilver could fit the bill.
As with Mercutio, you could also just separate Benvolio's name into Ben Volio. As befits his character and the meaning of his name, he wishes Romeo well. You might play on that idea and call him Will Wisher.
Likewise, Tybalt could also easily be divided into Ty Balt. Given the fact that Mercutio calls him the prince of cats ("More than prince of cats, I can tell you."), you could call him Ty Katz or Ty Baltenkatz.
As for Paris, he's the trickiest, but if you wanted to be really fun you could call him Paris Hilton. He does think he's "hot stuff" after Lord Capulet tells him that he can marry Juliet.