GV Captain reports his First Officer missing a position report to New York Oceanic while he is on a lavatory break.

Narrative

We were level at FL450 at cruise. I got up from my seat to use the lavatory. While I was up a passenger asked me to help with the aircraft's entertainment system. I was out of my seat for less than three minutes and then returned to the flight deck. After getting back in the cockpit I asked the First Officer if there had been any changes with ATC while I was gone. He replied no. Shortly after that New York Oceanic called over the HF frequency and asked if we had our position report over ONGOT intersection. I noticed that we had already passed ONGOT and OVEBA intersections. I asked the First Officer if he noted the time and fuel on the master document over ONGOT intersection; which was a compulsory reporting point. He replied no. We had already passed OVEBA intersection which meant that we could not see the time we had passed ONGOT intersection in the FMS CDU. We could compute to the best of our ability but it would only have been an educated guess. I responded to NY Oceanic that we could give them a position report over OVEBA instead. They replied and said to go ahead with that position report and that they would get back to us if they needed more. They did not. The flight proceeded uneventfully to the destination. I think the solution to preventing this from happening again in regards to missing a position report is if either pilot has to get up from the seat; that a brief of tasks that need to be accomplished while one pilot is away from the duty station should be accomplished. Also to not be complacent in completing the master document tasks at hand regardless of what oceanic airspace we are in. We get so used to flying worldwide in oceanic airspace that it becomes routine.