There is a similar application wherein the GUI is used to modify the PWM of the led through USB HID interface for data transfers on PSoC3/PSoC 5LP devices. You can find some inspiration there. Link: http://www.cypress.com/documentation/application-notes/an82072-psoc-3-and-psoc-5lp-usb-general-data-transfer-standard-hi…
However, I do not have anything similar for PSoC 4 BLE, but you can replicate the same and then use the same GUI from the above project if you do not want to build from scratch. I will try to do the same on my side. Do let me know your observations.