The standard gambit rules are that each player with at least one figure, that is worth at least 5 points if eliminated, within 3 squares of the center of the map gets 5 points.

So if you have a Mouse Droid within 3 squares of the center, you get no points.
If you have a Clone Trooper within 3 squares of the center, you get 5 points.
If you have three Clone Troopers within 3 squares of the center, you get 5 points.

You can do 'first player to score X number of points from gambit' or base it on number of turns.

You'll want to decide how contesting the hill will work; whether it just prevents a round or points from counting, resets, or turns back control of the hill.

Another variation you can try is having the hill be dangerous. I used to do this for MechWarrior, where the winner was the one with the most points at the end of the designated time limit. The hill was made up of 5 levels, each of which was more harmful to the pieces, but also worth more per round. So you were safer in the 4-point ring than you were in the 5-point middle, but you were also scoring less points. There was a 1 in 3 chance each round that every figure in the middle would get damaged. 1 in 6 chance in the 4-point ring.

Try out whatever seems reasonable, and don't be afraid to change it up the next time you play the format if you decide that something about the previous version of the rules didn't quite work out the way you wanted, or was badly abused by players.

One thing we have done in our group for multi-player games is a variation on attacks. Once you defeat a piece for a player, starting with your next activation, you cannot attack that player's pieces again until you defeat a piece from another player. This counts for Attacks of Opportunity too. Whoever defeats the piece finally gets the points for it - high score wins. It is a lot of fun and can change strategy in a hurry as you switch targets all the time.

If you are looking for a fast game with lots of combat, try using the Rattatak Arena map. Each player starts at one of the four main doors (three square ones) and nobody is allowed to leave the arena. Not really capture the flag, but variations you might consider.

There were rules from the Ultimate Missions somewhat for cature the flag. You place a 1x1 tile (the flag, etc) somewhere on the board (near the center if possible). A character must be adjacent and replace attacks to pick it up. Place the tile on the player's card. The object is to remove it through the player's original starting position before getting killed. A defeated piece drops the tile in its vacated spot and someone else can grab it. The trouble with this if played with no squad restrictions is the massive movement breakers have a huge advantage.

My favorite map for multi-players is this one from the Armored Cartographer's Map Pack 4 (not sure what the official name is, but the image is from miniaturemarket.com):

Also I had considered doing a rebels/imperials/bounty hunters 3 way scenario. Using the death star map to release/hold/capture a diplomat held in the cells

We always play either Rep/Sep/Fringe or Reb/Imp/Fringe when we play 3 players (since I almost have nothing from the 2 other eras) but never thought yet of using those cells, there's surely something to do with that. I guess the diplomat can become a "kind of a" flag.