People tend to avoid this one because it tends to behave eratically, but after a few minutes of staring at it I thought of this:
Giant Sandworm stands still for about 7~8 seconds after every use of its Stampede skill, I can make the most of that time by using Charge and Bash (x2~3) (using a Very Fast speed weapon [x2]) before Playing Dead until he Stampedes over me again, repeat as necessary. (Other skills may be used instead of Bash, but it appears to be most efficient at the moment)
Giants cannot Play Dead but they can simply equip a Vales Shield and load Defense instead, although in this case it is possible that the Sandworm may choose to attack you with Headbutt instead. Be careful when this happens because it can hit people in a certain area around it and can hit any players who are Playing Dead as well.
[video=youtube;9EvkojGE9ew]https://www.youtube.com/watch?v=9EvkojGE9ew[/video]
And voila, no hits taken and no bones broken! (except for his, but he might not even have bones)
I suppose he's only good for the occasional Violent burn and Used enchant though.
TL;DR: Charge - Bash - Bash (- Bash) - Play Dead, repeat.