You guys should really get with the times. Solo SCUBA diving is becoming more and more accepted. It can be just as safe as buddy diving and depending on who you are diving with...safer. As with everything, it may not be for all divers but I wouldn't think bad things just because it isn't for you.

PADI Self-Reliant Diver - http://www.padi.com/scuba-diving/padi-co...ve-specialties/

SDI Solo Diver course - https://www.tdisdi.com/sdi/get-certified/Solo-Diver-Course/

NAUI - http://www.nauisa.org/archives/solo.html

https://www.tdisdi.com/the-self-reliant-diver/

But to help address your concerns. I would get a plan together ahead of time and just designate the sites, days and times he wants to dive. Maybe 2 sites with 2 dives at each site (4 total dives) over the week? Realisticaly you're just talking about a few hours out of the whole week and if you plan accordingly you should be able to work that out.