I may be off base, however, I believe Stomp B was added to "extend" Stomp A capability, not as an isolated stomp location. My thought would be that you need to have a identical FX block. For sonic constancy I would put it next to the block you are talking about. Then the first FX block has a footswitch assigned in Stomp A and the next FX block has a footswitch assigned in Stomp B. Maybe not the most elegant method and you wouldn't be able to change them both at the same time in both stomp areas. There may be others that have a better method that does work. If so I pray someone adds more thoughts to your question.