I guess I don't understand what problem you are trying to solve here - I do not see one to solve. EA26 will try to process all available billing documents. If 50K are available then they will be invoiced; if 70K are available the next day then those are processed. Beyond that, you cannot execute parallel transactions for any mass activities as you will get locking errors - and will result in even fewer results than keeping it as is.
regards,
bill.