Start all your Flying shots with low power and gather lots of Daredevil Icons on your way to the target. You have lots of Walls, pillars and towers for this.
Also, try to get to the goblins on the bridge to terrify and "headshot" them.
Gather as many 5K icons as late as possible, but gather as many as you can.
Guide this one in to the upper middle platform of the bridge. This will make one side of the bridge colapse. (Just tried to destroy them both several times, but always failed.) Maybe try using the speed icon?
This will bring your Multiplyer to somewhere close to three time muliplyer.
Don't forget to start with low power and to gather plenty of daredevil icons. ;-)
Stick to the left and guide this one all the way to the end and make it detonate right next to the left tower in to the wall on the left side of the dynamite. This shot must blow up the tower and the bomb.
Multiplyer must hit the "x4" mark.
Guide this one on the right side of the map diretly towards the wall and make it explode on the right side of the very left "tower platform" with the goblin, starting a little chain reaction to the right side. This shot must destroy the complete wall and the right tower.
Multiplyer hits "x5"
Eays peasy! Use Split shot to destroy the buildings in the front. If possible, hit the goblin and let them all bounce from the ground to net 4 bank shot icons.
This will bring the Multiplyer to 6 and shoud earn you the gold medal.
Hope I could help! :-)