Typically you need to set your macro so that the Weapon Skill goes off before your first strike triggers after activating Sneak Attack. If I'm recalling correctly, two seconds' wait is usually correct. Thus, the macro would be this:
/ja "Sneak Attack" <me>
/ws "WS Name" <t>
Remember that the Weapon Skill needs to strike the opponent with a melee attack (you've noted this in your title), Gust Slash won't work with it (though I believe the SA persists until the next melee strike).