On my provisional my sisters friend signed it and put occupation as 'shop asisstant'. I did at first think it would have had to be someone such as a doctor etc but obviously not.
It would be cheaper to get a renewal. I lost mine and forgot what adress I'd given or any details of the license so sent of as a new application. They wrote back asking if I was the same person as what was on their records and later refunded me the amount I'd sent and just charged me the renewal price.