The guys at Beastmaker have some brutal training trips for finger strength.
I like to post stuff like this up here as it means that I can browse these ideas on my phone when wanting to pull down a 'random' training program. I was thinking of 3-5 sets of 3-9 second hangs with rests of one minute in between sets (all on one arm at a time - if possible).
4 finger open hand large hold
4 finger open hand small hold
3 finger open hand - front
3 finger open hand - back
3 finger open hand - front - smaller hold
3 finger open hand - back - smaller hold
4 finger half crimp
4 finger full crimp
2 finger pocket - back
2 finger pocket - front
Although the goal is one armed hanging, it is possible to set up bungies or a pulley system to offset the strain. You could use two arms for some of the hangs, but one arm training is more intense due to the bilateral strength deficit- the difference in maximal or near-maximal force generating capacity of muscles when they are contracted alone and in combination with the contralateral muscles. (i.e. you might be able to perform a pull up with twice your bodyweight, but that does not mean you can do a one arm pull up).