Reducing Lightmass baked AO only for selected objects in a scene?

Hey there, is there a way to exclude/reduce the effect of lightmass baked AO for selected objects in a scene?
In specific, I have a stylized tree which basically occludes itself too much in between the lots of crossed tree planes/leaves and therefore gets really dark in some places.
Any ideas how to reduce the AO there?

you can generate a custom AO for the tree, I know that you can generate the AO easily on speedtree and import on unreal