[Suicide Junkie]

You could try using the map editor, and giving all warppoints in the player's start system a cloaking ability.

Human players would just spend a few turns giving orders to "warp" at every square on the edge of thier home system until they find one...

You could give all warppoints cloaking abilities, which would really slow a player's expansion down, but once they have discovered by chance where a warppoint is, the movement AI would direct all ships straight to the right place.


How about this for another alternative:
Using the map editor again, remove all warppoints from the player's start system. Add a new system right beside it, with connections to the homesystem and some other nearby systems.

Now, the player is forced to be a neutral until they develop advanced stellar manipulation tech, or, research a new tech area.
This new tech area would be "warp point detection", and would give a component which can open a warppoint to the next-door system only (range 1). The player "finds" a warppoint to the next-dor system, which allows them to expand normally.
You could say that the warp point detector is a prototype device, and only needs to be tested. Maybe the big detector component is just used to find the characteristic "frequency" common to all warppoints. Once that is done, all ships get free, fully operational detectors, and the game continues normally, with your race expanding into the unknown.