As Jay states, CYOA is on top of this requirement. On my clearance to Culebra in March, the C&I officer in Puerto Rico that I called enroute to Culebra required that I first be anchored (we went to Ensenada Honda) and then call back with our info. This was done with no problem and then I received a call back from the local Culebra C&I office with our clearance #.