You won't be able to split the payment between two credit cards using the TurboTax system during e-file. But, you can when you pay directly to the IRS. Select "Pay by check" when e-filing and a voucher for the full amount will be produced, which you can then ignore. After you e-file, you can use the website below to make two separate payments with a credit card directly to the IRS.
https://www.irs.gov/uac/pay-taxes-by-credit-or-debit-card
