What about something like this it would allow you to strap to the tree and have a rope adjustment all in one shot. I was thinking if you sew your strap end to the center bar it would allow you to up and over with the loose end of course the bend in the unit should be optimized to the angle at wich your hamock hangs and you might want to set up your hammock and use a bevel guage or compass to get the appropriate angle I'm guessing that it would be right around 30 degrees. I think the angle would allow you to have a straight buckle to the tree with out adding tention to the plate and forcing it to dig into the bark of the tree. So what do you think?
I have another idea and will post that after I go paint myself another picture.