Punt,
Slowly.....if Blackrock had been equipped with a Transponder as is generally done with Oil Rigs and Platforms......and you had your Radar appropriately set up.....then that bit of Rock would be very easily identified.
If you had included Blackrock as a Waypoint the GPS would point to it as well.....and with a moving map display there would be a third way of identifying it....and with a Minimum Crossing Altitude/Height....in a preplanned Approach Procedure.....then by adding some Structure to an Arrival to Blacksod.....safety would be enhanced....would it not?
What technical issues (if any) prevent the Irish Light House authorities from installing the Transponder?