I've heard from other PF'ers that Chanel eye makeup remover works wonders w denim transfer. I used my own Dior eye makeup remover & it worked very well on my pink fluo mini. Can still see a smidge if i look really closely.
I've also heard baby wipes are good. To protect it after cleaning try grabbing some leather protector such as Collonil organic line. I use their cleanser & protector on every bag I own! From lamb skin to leather to suede to nubuck, this stuff is wonderful. HTH!!