I don't think it's possible. For all I know, the end turn of 2020 for score purposes is embedded in the game program itself. However, if you check with the manual for the individual score components, you should be able to compute the scores by yourself.
The components are (from memory):
- Each citizen adds 1 point
- Each happy citizen adds 2 points
- Each wonder you possess adds 20 points (560 points max)
- Each polluted square subtracts 10 points
- Each future technology discovered adds 5 points (1275 points max)
- Each consecutive turn of peace adds 3 points (100 points max)
- Points are added/subtracted for Barbarian activity level (-50 -> +25)
- Up to 400 points are added for succesfully landing your Space Ship on Alpha Centauri
Now, to get the percentage score, you'll have to calculate in the factor for the difficulty level you're playing. These factors escape me for the moment, but perhaps others can help out?
