Hi Dharmakasi,
your requirement is little storage to me in casecustomers using same business role in this case you can only achieve your requirement by PFCG role. I don;t think there is some other way because on some criteria you need to separate customer 1 to customer2.
I believe PFCG role will be the best way or if there is a scope to create a new business role or else new business role needed to be created which you can assign directly to user master record SU01D in CRM_UI_PROFILE to meet your requirement.
Thanks,
prem