I've quickly came up with this
http://db.vanillagaming.org/?talent#f0xfojxZMhVZxrfoc for the sole purpose of imp sap as u requested.
Tho you havent been specific whats your gear like nor what's ur faction. This spec could be sort of useful with 60's starting gear as your physical component of damage will be less valuable than your magical one at this gear levels, hence the poisons (2x instant for trash and low HP mobs or some combination of utility poisons, and instant/deadly for single target bosses/large HP pool mobs).
Also its lot stronger if you are playing a human rogue cus of that extra weaponskill. Otherwise u should probably go daggers and get DM belt or that offhand dagger with weapskill.
As your gear improves, id definitely aim transitioning to more conservative specs. Note that imp sap is only as useful, as your tank may just yolo it in and pick up the mobs as u got unstealthed. Or on chained packs u may just sap>vanish and let him do the pulling.