PSoC Creator provides a simple way to implement certain type of USB device including a USB composite device that has two CDCs. You can turn a $10 PSoC 5LP stick into a FT2232 like device or you can build a UART sniffer with few lines of code.

(Select a Component) Start a new PSoC project with the selection of appropriate PSoC device. Then pick a USBFS from the Cypress Component Catalog on the right.

(Import Descriptor) Open up the configuration dialog by double clicking on the component. At the Device Descriptor page, select the Import Descriptor Root (green down arrow) button. It will show up a file selection dialog box that allows you to import templates (xml files) from handful number of predefined settings. For the purpose of this post, choose the file USBUART_TwoComPorts.root.xml.

You will find that all the descriptors and items necessary for dual CDC are nicely populated. You can delete any existing device descriptors.

(Two UARTs) Finally populate two UART components and set their parameters such as baud, number of data bits, parity types to suit your purpose.

This component is initialized with the same way as any other USB component. However you need select one UART port before calling USB UART API for communication. (source)