Just let the Evangelicals know you are there to inform them about jw's and not to discuss the bible on a personal level. Once they hear about jw's they will not be surprised that you and many ex jw's become atheists. I had one minister tell me once that Mormon's & Jw's produce more atheists than anyone!
Most people do not know anything about jw's, you would be doing a great service in my opinion. The biblical doctrine stuff they can look up anywhere and discuss with their minister or at their own bible studies, what they have no idea about is all the unwritten rules and the read between the lines stuff. The culture of dubland itself, the heirarchy, language barrier when discussing with a Christian, family life, pedophile/two witness rule, that many ex jw's are diagnosed with ptsd, life for a jw child, marriage within the jw's and when one leaves, marrying a jw, love bombing, baptism into the org, etc..etc..etc... and let's not forget shunning!!!!
Have fun and make it clear to them what you will be skipping if you don't want to go to something, spend that time in the hotel pool or something.