AwSnap: First off, there are a LOT of complicated details around the chronology question, but i would say that the complications arrise from apologists who try to sidetrack the argument into needless details because the facts are against them. If you go into these details you need to be very bright and brave to look through the smoke. I havent gone through the process, but i doubt i would have been able to do it :-(. However, and i say this as an atheist, i think the bible is pretty clear on the point, so thats the route i personally have desided to go.
First make them agree to the statement: 'there are no secular evidence (historical, archeological) which point to 607. Everything point to 586-7'. That should be quite easy, since its pretty much written directly in 'insight to the scriptures'. Notice there is a lot more evidence than described in insight, and what they write about get the usual 'jw treatment', but that is a side point. Anyway, now you can properly make them agree that the only reason one should accept 607 is because the jw view of jeremiahs 70 years is the only one supported by the bible.
This should open up to the second part of the discussion: The jw view of jeremiahs 70 years. here you need to go into A FEW details, since you need to know both the jw view of the 70 years AND one or more alternative viewpoints to get a proper understanding of it. Fortunately this is quite easy, but it needs to be done. Basically the questions you need answer to is: (I hope my suggestions are right, please check it for yourself!)
a) What did the 70 years consist of? (jw: Total destruction, alt.: a CONDITIONAL prophecy with 70 years of servitude to babylon, destruction if jews did not comply, but in all cases not complete desolation of every person in judea)
b) To whom did it apply? (jw: Only israel, alt: a lot of countries as the bible say black on white)
c) When? (jw: 607-537, alt: 609-539, 70 years in all instances)
d) What event define their beginning? (jw: hell of a good question, i believe they think it was a particular deportation to egypt, but you might want to ask your friends. alt: Babylonians arose to world domination)
e) What event define their end? (jw: Jews praying at a specific temple site, alt: babylons fall and daniel praying for forgiveness).
After you got these answers pegged down both on the jw interpretation of jeremiah and the 'alternative', you are in for a real shocker: no big book are required, just pick up the bible and read the book of jeremiah (which must be the ultimative source on jeremiahs), especially the chapters after 25. Keep the above answers in mind, and ask yourself which viewpoint is the most in line with the bible. It was a great surprice to me how easy it all fit with the non-jw viewpoint, for example the image of the wodden and iron burden jeremiah put around his neck.
I think that is the path you want to stear them unto: Ask them to answer questions a-e) above based on the bible, perhaps offer quotes in the bible that are not in line with the jw point of view.
To flesh out what i have called the alternative chronology, you should read this excelent book compiled by Doug Mason: http://www.jehovahs-witness.net/watchtower/bible/186301/1/New-study-on-the-Babylonian-Exile-and-without-chronologies , he also wrote a couple of great posts a couple of months ago with 'hard' questions to the jw chronology.
JW litterature is IMHO not that inconsistent when it comes to chronology.. its just horribly complicated, confusing and leave out all the important stuff. Thats why i recommend the bible. One thing in print they get 100% wrong though: The king list from 539-607. If you ask them to tell you when the kings ruled, they wont be able to do so because its hidden very well, and if they finally manage to do it, the king list will point to one date for the fall or jerusalem: 587.
I hope i didnt stray to far from the spirit of your question... and i hope i am correct with regard to my answers to a-d)! its a couple of weeks since i read up on it last time :-).
Sincerely and please write how it went if you feel like it!