im pretty newb when it comes to nurbs
but i belive you can use the Loft option to close off the sides.

Also, if you go into select by component and deselct "Select by Component type" and click on Select By parm points"

You can click and drag the yellow dot to each of the corners of you guitar head....once you have done this too all the corners where you would like to detach, select all the pieces again go to "edit curves>rebuild curve> options" and in the "Number of Spans" put 10 (or play aroun with this til you get it good, im still newb like I said so I am telling you by what I have done for some tutorial from a book I bought)
After Rebuilding, keep the curves selected and go to "Surfaces>Boundary"
This way you can fill up the top portion of the head.......I hope you understand me, i kindds suck at giving good written instructions.

I hope this helps, and if anyone can suggest something better....THANKS!! lol
Anyway good luck with that dude, i impatiently await this finished product.

oh and Blink ROCKS!