I would review the actual need of your requirement. What is the information that needs to be displayed for each customer and rethink the design in order to achieve the needs.
One possibility would be that you get a column indicating the customer and then you just append the records corresponding to each one regardless how many you have in the end.
Another possibility is that you have an initial ALV with the general information of each customer and then, when you double click one line, you access the second ALV with the data corresponding to this particular customer. This can be done through events on double click in the ALV. You can either have the data to be displayed in the second ALV in an internal table for all the customers and just filter and display on double click or you can select, process and display the data on double click. This depends on the particular needs of the requirement.
Hope you can give more info about the scenario so that we can think of the best solution.
