came across this app just now, you have to donate to get it bigger than 500pixels but it seems to work pretty well once you do, obviously its not quite as robust as photomatix and even photoshop but its simple to use

note if you want to try it once you want to export you have to goto file, plug in extras, then enfuse ... I actually had to read the documentation to figure that out :)

http://photographers-toolbox.com/products/lrenfuse.php?