Section 226.14(c)(3) seems to fit the situation you describe.
If the finance charge imposed during the billing cycle is or includes a charge relating to a specific transaction during the billing cycle (even if the total finance charge also includes any other minimum, fixed, or other charge not due to the application of a periodic rate), by dividing the total finance charge imposed during the billing cycle by the total of all balances and other amounts on which a finance charge was imposed during the billing cycle without duplication, and multiplying the quotient (expressed as a percentage) by the number of billing cycles in a year, except that the annual percentage rate shall not be less than the largest rate determined by multiplying each periodic rate imposed during the billing cycle by the number of periods in a year.
Also see Appendix F for illustrations.
_________________________
...gone fishing.