I'm trying to remove the right front link in order to change the half-shaft. However the knuckle is turning in the socket and I don't see a non-destructive way of holding it while I spin off the nut. Any suggestions?

 

I do not remember having to remove the front sway bar link in order to take out the driveshaft but has perhaps been too long. Check the end of the link stud and there is usually a place to insert an allen wrench to hold the link stud if the nut is being stubborn. If you can still get back tight then do so and then clean the threads throughly with a wire brush and apply some WD-40 or equivalent to the threads before attempting to remove nut.