th respect to a consumer credit sale other than one pursuant to a revolving charge account, the seller or his transferee may by agreement with the buyer refinance the unpaid balance and may contract for and receive a credit service charge based on the amount financed resulting from the refinancing at a rate not in excess of that permitted by the provisions on credit service charge for consumer credit sales (§ 2201). For the purpose of determining the credit service charge permitted, the amount financed resulting from the refinancing comprises the following:
(1) the amount which the buyer would have been required to pay upon prepayment pursuant to the provisions on rebate upon prepayment (§ 2210) on the date of refinancing, except that for the purpose of computing this amount the minimum credit service charge that may be retained pursuant to § 2210(1) shall not be included; and

(2) appropriate additional charges made pursuant to § 2202 but not paid in cash by the buyer.