How to make CallRail the default calling app for Pipedrive CRM?


Does anyone here use Pipedrive CRM with Callrail? If so, does anyone know how to set Callrail as the default calling app for Pipedrive so that when you click on a phone number it opens Callrail dialer? Pipedrive has a section to set a custom default calling app (like Skype) but I can’t figure out the correct code or protocol to plug in to make Callrail the default. Its supremely frustrating because it seems like it should be simple, especially since both have really open API’s. Any help would be greatly appreciated. Thanks