I haven't been out in FS for 2 years now and I haven't received 1 sheperding call or inquiry as to why. Guess my elders don't care about me. boo freakin hoo.
I would say as little as possible. Tell them you have been overloaded with work or family issues. They will probably read you a bunch of scriptures about why preaching is a christian responsibility yadda yadda yadda. Just smile and nod. Tell them you'll pray about it and wave goodbye as they drive away.