Are your goals still running related?
There are a number of pull-up challenges that can be really enjoyable and a change of pace otherwise.
One that comes to mind is you do a number of pull ups on day 1, say 5 sets of 3 for 15 total reps, then add 1 pull-up every day for 100 days. You can add more reps, more sets, split workouts AM PM, do them through the day, as long as you do them and add 1 per day.
I did a similar thing with close grip press-ups to bring up my triceps.