For the record, quite a few solutions were proposed which should work.

The first approach I will is drilling & reversing the J.
However that greatly changes the geometry, and may need side braces.
(DTV-AT9-SB Standard Short Brace for DIRECTV Slim Line Dish DTV-AT9-SB)
http://tinyurl.com/9cmr8l6

So the second approach is to find a SECOND Dish-TV J-arm and mount them
both on the wall, one ABOVE the dish and one BELOW (in opposite
directions) with the "tops" of the mounts almost touching each other.

The third approach will be to shove 1 1/4" EMT electrical conduit into
the short end of the j-arm and then weld it on or bolt it on.