How to use Unity Sprite Packer for Tight & Full Rect sprites at the same time?

I'm using Unity's sprite packer, and I need one atlas to use the default packer policy (full rect) and the rest of my atlases to use the tight packer policy. Changing the built in setting appears to apply the setting to all atlases. How can I specify this per atlas?

Thanks!
Ray

PS -- the reason I need one of my atlases to use the default/full rect policy is because NGUI doesn't seem to like Unity sprites that are tightly packed.