My heart goes out to you both - I still remember the odd days when I'd sit at the kitchen table, stariing at my leg thinking how I didn't want to do it.
If he's not allergic to any of the ingredients in Anbesol or Bonjela, you/he could try dabbing some of that on the 'chosen' spot just before injecting - they contain lidocaine (amongst other things), which is a painkiller. Anbesol is better as it's a liquid.
That can be a short-term fix - it dulls the injection site and so can remove the fear of pain.
The other thing you can try is to get him to 'feel' for the best place - even now, after 37 years of doing this malarky, I still find times when the area I've chosen for the cannula (I'm a pump user now, but the same applied when I injected) is just not receptive to the needle - if I ignore the feeling, it hurts, whereas if I spend a little longer 'feeling' for another site, that generally produces a much more harmonious result.
If he's into Star Wars or The Hobbit, etc., he could try picturing his search for an injection site as a test of Jedi / Elvish strength.
I'd also look at where he's doing it - as I mentioned, when I was a lad, I did it in the kitchen (the insulin I used then had to be kept in the fridge), which used to make it a big deal because everyone else would be in the lounge, etc. so it could be that letting him chose another room to do it (perhaps in front of the TV for example) would aid his mindset.
It's not easy, I know, and it's still very early days for him, but try not to get over-anxious as that can work against you.
Do call the Paediatric Diabetes Specialist Nurses - they may have tips or support mechanisms in place that can help you all come to terms with the diagnosis and treatment.
Lastly, get in touch with your school and get an Individual Health Plan (IHP) set up for him straight away - from September it's a legal duty for schools to provide support and equal opportunities for children with diabetes. See this link:
http://www.diabetes.org.uk/Guide-to-diabetes/Schools/