Depending on what type of tree you're building in, bolts may actually be better than a rope/sling/external type of attachment.
For instance if you're using a live oak (I think I remember you saying you're from Texas?). Live oaks compartmentalize very well (that means they do a good job of fighting decay fungi). A few eyebolts or J-lags are not going to harm the tree much at all, if they are installed correctly. In time the tree will just swallow them up. Rope/slings, on the other hand can do serious damage to the bark and cambium of a branch if they are allowed to rub under load or have large loads pinching in one place, which will cause much more serious and permanent damage to the branches.
I'm not trying to discourage you here. I'm sure there are creative ways to do this without bolting into the tree. I just wanted to give you a little bit to think about. Ropes can hurt trees too.