This doesn't really fit into the exploitssection, so I put it into the guidessection, although it's more like a Tip than a real guide.
I used the searchfunction but didn't find anything like it.
I wouldn't consider this common sense. I found it out by accident and then tested it a few times. Worked everytime on the Dun Baldar North Bunker, haven't tested the others yet.
1. Be alone around the tower you want to tag
2. Gain aggro from the guards and enter the tower
3. Tag it
4. Move away from the tower till you get out of combat
If you were the only one on the guards aggrolists they should be despawned by now.
I know that this is not interessting if you can kill the guards easily yourself, but this is maybe something you will find useful as a healer or with an lowlevel alt.