If it is empire score then lots of mothballed ships which unmothhball at the end game will do it, but you must be able to pay the cost to unmothball.

If it is the racial experience score you find by examining "our race" then that gives some points for building a colony ship and another 100 when it colonizes. So you could colonize no population then abandon planet and keep doing that till you ran out of patience. I am not sure if the abandon planet is negative to score, check it out.
I once tried to figure out what all gave me racial experience but at that point in the game there was too much going on to figure it out and it was not really all that interesting to me...

By the way, I just posted a map on the maps/scenarios forum which may be useful....

Has the AI been changed to use solar sails on high tech ? I just ran a play test of my map using the standard 1.35 and all the AI designs had quantum reactors and max engines but no solar sails, which is dumb. They also were ignoring the sphereworlds to colonize ruins worlds which was REALLY dumb. Possibly because of atmoshere none but even with the wrong atmosphere the sphereworlds are the best thing they could find. It needs fixing.