You can take the webbing out, double it over and tie knots in it. At the hammock end, tie a loop with some other webbing and onto this you can attach a karabiner. The original webbing then wraps around the tree and you have small loops to attach your karabiner into. Here
's a better demonstration.
you could ditch the DD webbing and get some climbing tape. You can get some from Urban Rock
in London. You could use this tape with the karabiner or get some descender/rap rings.
I think the lightest option in going with the whoopie slings.