Where is the selection for 'flogging a dead horse'?
Seriously, this is unneccessary, and silly. And never berate someone into doing something of this nature. If he wants to, he will. Otherwise, just leave it alone.
Injections are easier on your liver, and give you a broader range of gear to choose from. Neither of these factors are going to be more important to your buddy than his fear at this moment.
If at the end of these 6 weeks, he is not asking where he can get some syringes, then you will know gear is not for him, and so will he.
It will all work itself out in time.