How to manage billing for multiple store under the same account?

[Vivasoft]

Hi there! Our team at Vivasoft has run into a blocker and we would like to get enlightened regarding the issue we are facing. How can we manage billing for multiple stores under the same account? Our application, Poptrigg  allows merchants to add one store in all our current plans, however we want to add more than one store under the same account in our paid plans. Since Shopify’s billing is store specific, we don’t want to charge extra for each new store added to the plan. Any solution or suggestion is welcome. Thank you!