i know this is an old topic but here's my two cents:
I use Horween Dublin, Essex, Chomexcel etc. for my wallet interiors and have found that the only reliable way to "split" the leather is with a Little Giant Razor Blade Plane from the 50's & 60's. It takes a little practice and alot of cursing but once you get the hang of it it goes pretty quick... helps me take 4-5 oz. down to lining thickness.