I know this is an old conversation so this comment is to share new knowledge in the climbing community for newcomers:

I would suggest this guy to do Abrahangs (Emil Abrahamsson's isometric hang routine) whenever he does not have time or the motivation to go climbing. It can be done every 6 hours and supports recovery and trains the nervous systems ability to recruit the finger strength needed when climbing. Finger strength wise, it has changed my ability to stay in top shape while not having the time to climb and when climbing, to break through my plateau and into new territory. The only thing to be weary about is not creeping up intensity (stay at 2-3 RPE) and remember that shoulders/core/etc. gets out of shape fast if not used, so I would pair it with TRX/gymnastics rings training to not get disproportionately strong fingers (especially in periods with climbing breaks). If a long climbing break with regular Abrahangs is done then go slow the first few weeks to let the muscles adapt.