I came across this today and apparently they are in wide use back where I come from with the "overland crowd". Its a old tech item from sailing that has stood the test of time. I'm not sure I like the price, but its not outrageous for pre-made. Making your own seems possible given the ideal rope. I can see having one of these might be handy for those few situations where a proper shackle wont work right. Obviously you would want to take precautions if it were to break though.
http://www.softshackle.com/Shopping-cart.html

http://lucky8llc.com/Products.aspx?P...09#prettyPhoto
http://l-36.com/soft_shackles.php <----uses Amsteel line like we are used to seeing in nice winch lines.
https://www.youtube.com/watch?v=jH66tGsWv_Y
[img width=800 height=600]http://www.lucky8llc.com/ImageUploads/ProductID7209ImageID6027.JPG[/img]