That's not strictly true in general here, Sandy, but we can make it so for this trip. The BH dive is generally done in one group surrounded by all the DMs and no operator likes or will usually permit someone to "do their own thing". The general rule is go down with the group or don't go down at all. However, I'll offer my services to accompany anyone who doesn't want to go all the way to 130ft+, and although Amigos del Mar don't usually welcome me on their boats as anything other than a regular punter I'll make sure that this dive is different - if we use Amigos. Kamala might prefer to do the day trip with her new friend Andre...? With his business I can do anything (responsible!) I want.
A point on nitrox. There will be an analyser at the dive center for people to analyse (and then mark) their own tanks, so I don't see where the risk comes in. At least there should be, and if there isn't I'll provide one.
Thanks for the info Peter.