Jim,
As others have told you the proper procedure is to disqualify B1 BEFORE the 1-and-1 is administered and his replacement will shoot for him.
However, I thought that I would point out a nuance for your edification and amusement since it happened to a friend of mine.
Same play as yours, but the scorer fails to notify the officials that the T is B1's fifth foul until after she has shot AND MADE both FTs due to the personal foul.
By rule, B1's points stand in this case. Since the officials did not inform the coach, B1 was never disqualified. (4-14-2) You will find this stated in 2-11-11 Note 2.
Sadly, my friend thought that it was a correctable error (wrong player shooting) and wiped out the points and reshot the FTs with the substitute, who missed them both.
We got to tease him about it for quite a while though.