Have two assassination attempts; one immediate, and one put in motion well in advance of the the immediate one.
[EDIT] This does rely on a literal interpretation of the following;
usually precogs only see about two days in the future and only things
that happened to them or to someone that they are closely connected to
Suppose you know that the rebel leader will be in an office building/shopping mall at a specific time. You make plans trigger the fire alarm and kill them at the building's fire evacuation point. The precogs will see it, warn the leader, who will logically stay the hell where they are during the alarm.
All is going as planned.
Now you plant a bomb where the leader will be - or rather - you planted a timed bomb there a fortnight ago. Well beyond the horizon of the precogs' ability to anticipate.
The logic for this goes like such; the fire alarm poses no direct threat to the leader, nor does going to the evacuation point. There are many things that would influence the leader's actions, and most of these would slip past the precogs' attention. Mundane things like what the leader reads in the morning paper, or the weather report on the nightly news.
If a fire alarm is triggered, but no assassin is present, then the leader is unharmed, and no more inconvenienced than any other person in the building. They survive the bomb because the normal, sensible, behaviour saves them.
Adding the assassin to the mix provokes a precog response: a response that actually causes the assassination.
[EDIT] Witnessing an explosion that doesn't harm you shouldn't be perceived by the precog bodyguards. Also, the bomb isn't the cause of the fire alarm, so there's an extra layer of disconnection between the two that helps conceal it from the precogs.