To be honest, the technique to cause the least amount of discomfort varies from person to person. I have found most of my patients (only one has ever told me I hurt) feel less if I apply firm pressure to the injection site for about 15 seconds and then quickly remove my finger and insert the needle and push the liquid in. The more you have to inject (volume wise) the more it hurts. Give it a whirl

Well done to your DH on doing the needle though, I reckon it's only natural for a partner to not want to give the injection.