I agree with two earlier suggestions:

1. Just set the camera to the fully automatic "green box A+" on the mode dial and it will revert to the standard method of AF with All Points/Auto Selection. It will also basically be fully auto exposure, according to whatever picture style mode you have set (one of which is Portrait) in the menu and you'll probably only be able to shoot JPEGs.

2. If you want to be able to use other exposure modes, save RAW instead of JPEG, etc. instead set up one of your Custom modes to revert back to standard (default) method of focus.... Your choice of C1, C2 or C3 on the camera's mode dial. You could also have this switch the camera to using one of the more automated AF patterns, such as All Points or one of the Zone Focus options. See the instruction manual regarding how to set up C1, C2, C3.

However you also could just temporarily undo the BBF setup... it's really not all that involved or difficult to change back and forth. You just have to go into the control customization menu and change the setting for the shutter button back to it's original setting. Probably the hardest thing about it is remembering to set it back!

With 7D-series (and many other recent Canon models), BBF is actually already almost completely set up by default. It's already set up to use the AF On button on the back of the camera. To use BBF, all you actually have to do is remove the "AF start" function from the shutter release. Pop into the control customization screen, first item is the shutter button, and the 2nd or middle setting of it is "Meter start". Select that and you're one. Switching it back normal AF temporarily is just the opposite.

If you (like me) swap the function of the AF On and * (AE Lock) buttons, it's a little more involved to switch back and forth. But it's still not a very big deal.

On the assumption that you're taking family portraits the focal distance should be the same between all shots so why not, just before handing it over, you do the BBF and pass it to them. I do this quite regularly and have never had an issue except for cut off heads, eyes dead center etc. The focus has always come out fine. Oh yes, do not make any mention of what you've done as it just invites lots of time consuming questions, not to mention they will, believing themselves to be the next Ansel Adams, want to try it out and invariably focus on the wrong spot.