Hi Jules,
You know the first thought that came to my mind reading your request is this:
Find all of the articles and information about people who have cured their cancer. See if you can get your dad to read them also. The idea behind this activity is to introduce the possibility of healing into your dad's awareness (to influence him).
I'm thinking of him having the mind set of "well, if these people can heal themselves of cancer, surly I can too..." is bound to produce the desired results of healing. It sounds like he's got the action and discipline part down, but he should investigate into his beliefs about him actually healing the cancer.
Try this article for a perspective...
Hope this helps,
Lil Chris