1) I'm not sure sustain is a problem with the LSR, as the reason that people have backed away from brass nuts is that there was too much difference in tone and sustain between the fretted notes and open ones. Jeff Beck does OK. However, LSR's are still really rare, if they were a huge improvement, wouldn't they be all over?
2) The graphite nuts are a little tricky to work with. Compared to bone, a file will just slip around at a certain amount of pressure, then start biting really hard with just a little more pressure. I've found it easiest to shape the grooves with abrasives instead, various grades of gray wet/dry sandpaper wrapped over a fret file, 6" steel rule, toothpick, etc.
3) Dan Erlewine has a pretty extensive section on nuts in his book "Guitar Player Repair Guide", along with everything you need to know about fretwork. Among his suggestions for making a non-locking whammy nut are details about carefully shaping the ramp up on the back side of the string, making the "break" point a little wider than you might think (so that no individual winding is likely to catch on an edge); most important, the slots for the wound strings should have a little flat in the bottom, instead of being perfectly rounded like a normal set of files will do. I've been able to muddle through with bone nuts doing the conventional stuff - straight string pulls, fine-polish the slots with 600->1500 grit sandpaper, and keep 'em greased.