Today I noticed with my lvl 80 rogue who are pushing some toons in scarlet, that u will gain Weapon Skill Points if you sap an enemy, had my Yogg Saron Axe in the Mainhand^^
so what u need:
1. Rogue
2. The weapon which u want to level into Mainhand
3. a hostile Npc
4. sap skill
(5.) G15 Macro keyboard which is hammering sap
happy Axe leveling xD