The location ZasterModa posted about above is a good area to do this.
In Frontier there is an enemy fort in the top left corner of the map. Find the fort and then head north. There is a small cliff that you can easily climb up to with a small enemy camp. There are two tents and two soldiers, one who stands on the edge of the cliff and another that patrols.
You can try throwing some bait behind the guy standing on the cliff, but you need to be careful. The first time I tried this, an elk ran up and knocked the soldier off the cliff. This did not count as it was the fall that killed him.
The second time I tried running around the area until some bobcats appeared. I threw some bait behind the guy on the cliff and also on the path of the patrolling soldier. There is a pile of branches you can hide in behind one of the tents. I jumped in there and saw a bobcat leap onto one of the soldiers and kill him.
Took about 10 minutes to get this.