Fwiw, it's not that easy finding examples of off-beat clapping in YouTube videos of African American choirs.

Here's one example:

http://www.youtube.com/watch?v=eSu6UtVImrQ
THE QUEEN OF GOSPEL MUSIC: QUEEN ALBERTINA WALKER SINGS!

One noticable example of off-beat clapping is the woman behind another woman wearing white blouse at 2:50 and throughout.

Btw, that song is "A Building Not Made By Hand". I love that song!

Also, see this example:

http://www.youtube.com/watch?v=z9Fyj27Lpww&feature=related
Hezekiah Walker & LFCC - "The Lord Will Make A Way Somehow"

The woman almost directly behind the soloist is clapping on the off-beat at about 1:43 of this video and at various times throughout it.