aggregation method subscription

Hi There,

I have specific business requirment where i have to bill to the customer based on Kilometer reading from thier BUS Meter, in subscription we have funcitionality of Asset Meter Billing,

But in my situation, i am not going bill specific Customer Asset but the aggregate reading of Bus Meter will be calculated and billing should be done on that Usage Quantity. Please guide if this is possible

In this attached Pic, There is Aggregation method colum, but i dont know where to config this value, The Idea is Sum the total of Meter Reading of Asset under one Customer Name. and The perform the pricing calculation on that quantity