There are several methods of working around Zone of Truth, but very few of them are mechanical in nature. The trick is the duration of the spell and the meaning of "a deliberate lie." Of course, depending on how brutal your players are, these may or may not work.
Speak like a politician. You can spend a lot of time saying many words that don't actually mean anything. So long as nothing you say counters the truth, it works. You can also imply things that aren't true, so long as you don't actually say them.
Don't say anything. Nothing about the spell forces you to speak.
Relate a story to answer the first question that takes longer than 10 minutes, allowing the spell to expire.
Answer every question with another question.
Speak only in half-truths. You don't have to reveal everything when you speak, just not a deliberate lie. Give away some information without giving away anything meaningful.
Believe the lie. This is actually hard for a BBEG, err... friend, unless they are a fanatic.