Just did a tour of Old San Juan, PR with a large group. Spend $500.00 or more with Viator (tour arranged through them) and get one mile per $ spent. Miles have not posted yet. The website says 4-6 weeks to post.
http://www.viator.com/earn-miles
They credit to United or Americans FF program.
Riding a Segway for miles works as my most unusual so far.