Non- 50:50 split

I am currently trying to siphon off a little iron from my belt into steel production, however I don't want to take 50% of that belt off. I would really like to only take around 10% of a belt.

With out a huge number of splitters is there anyway of doing thing? If it was adjustable too would be excellent.

If its a mod, I am not adverse either!

Thanks!