You'd need a double pulley though,

I have a Fixe pulley like this one=>(http://www.rei.com/product/635119?vcat=REI_SEARCH )that is wide enough to fit both ropes at the same time. Since you are not moving long distances away from the redirect point the amount of friction is very minimum and the main benefit is to allow the rope to follow you along in a different direction without dragging over several rough branches and in the case you loose control the distance from the redirected TIP to the climber is shorter and the potential for a mayor tree trunk hit is significantly reduced or eliminated. Using a Screw_link_ is definitely overkill in this scenario because even if the redirect where to fail completely you are still tied to the main TIP way up higher from where you are currently working. IMO.
This set up technique I used many times in a couple of large take downs I did on three dead trees in from of my house. I tied as high as possible and worked along large limbs way out and this gave me a lot of extra balance while making the cuts with both hands on the chainsaw.