Assuming you are calling the invoice 'ledger'? You can set the allowable amounts for insurance under Admin> Insurance. Select insurance, then go to fee schedule. For Medicare, we input the allowable amount, figuring the secondary will pay the copay. If we find that not to be the case, we have a cheat sheet with the breakdown of their coinsurance. Hope this helps!
Don't let what you can't do keep you from doing what you can do!