I think this would be a dangerous modification. I've worked on a good many exposed hammer rifles and the highest failure part is the hammer. More specifically, the half cock notch. Should the half cock notch break as it often does, the gun would fire when you pulled the lever up. Your safety information in your user's manual will usually state the half cock position is NOT A SAFETY.
You might consider a hammer extension. These are knurled devices that clamp on the hammer to make it easier to cock or release the hammer without slipping. Peterson and Uncle Mike's both make one for under 10 bucks that would fit your 1885s.