Convince your father why it would be beneficial for him. What does he have to gain?
This situation reminds me of one that I'm in at the moment. I want to add a smartphone to my family's plan for me to use, but my parents will not agree until I can show them that I can afford it and cover the monthly cost by myself. However, I have a consistent job with decent pay, so it should be fine. Basically, it's $30 every month, with the addition of the upfront cost of the phone. I have an idea to convince them to match a monthly payment of $15 if I give them a year's worth of $15 payments upfront along with the base cost of the phone. This is where it's worthwhile for them. They don't have to worry about their son being behind on payments, and I get a discounted monthly cost.
TL;DR? Make it worth their while.
