Hi Phil,
Go wash your mouth out with soap, "block" is a dirty word To me when you say "block" it invokes images of meeting force with force and that is something I try to avoid.
I can see several reasons for backing up the Bong with your Wu. However, to me, the Bong is a transitory move and should not be used to "force" anything. Of course, that is just me as I have always been weak and lazy so I try to do as little as I can with as little as I have.
Oh, fwiw, I have used something similar to a Kwan Sau in practicing knife reversals and in that situation two hands are definitely better than one.