Yes. Logon to your Giffgaff account and order another sim. Activate it in your fathers name with a £10 or greater credit, but don't buy any goodybag. Within 24 hours he will get his £5 bonus credit (so will have £15 minimum). You will get 500 points with you can convert into airtime credit or cash in around six months time.
As your father uses the phone he will just use up the airtime balance at the rate of 10p per minute. As long as he tops up every three months. Giffgaff to Giffgaff calls are free, so he can call you for nowt.
Tigga - Avon SR4 Rescue with 40hp Yamaha 2 stroke