Nike released the new iOS update for the running app and you can add a run by yourself officially now! (Nike knows: If you can't fight it, join it)
I have not tried this personally but from what I see, it looks quite simple.
You can manually add a run completed within the current year to your Nike+ account using the Nike+ Running App on any compatible iOS device. Here's how:
Tap the menu icon in the upper left.
Tap the "+" in the upper right.
Add Activity icon in upper right of app screen
Tap the field to enter your data
Add Activity screen showing fields for Date, Distance, Duration and Pace
NOTE: Pace will default to the average pace of all your previously synced workouts. When you enter distance and/or duration, your pace will adjust accordingly.
After entering your run data, tap "DONE" at the bottom of the screen.
Tag optional information with how you felt, terrain, and shoes worn. You can also share your activity on social media.
App screen showing optional tagging of how you felt along with a flat line graph of your run
Manually added runs will appear as a flat line in the map area, with time, calories, pace, and NikeFuel stats based on the information you provided.