I think, 4 would be more realistic, as you need some room for a bracket to hold them (as I expect you want to be able to change them without using tape). A special back-plate could be made to allow access to the battery compartment without removing the whole back (bracket could be part of it - 3D print as one). It’s nice that the size allows it… almost like it was planned… 
And about that picture… You mean like this?
Thanks @lipu - it’s not like we don’t have a month and a half to kill (at least)…