Scarring
I find it a little disingenuous to worry about scarring from a 31 gauge needle when people are hanging pounds of weight in hopes of making scar tissue to make their junk bigger. I would think injecting as close to the target as possible and using a ring to keep the blood there will maximize the uptake into the receptor. I’ve been reading about IGF and how it affects smooth muscle proliferation in the CC.
I bet a cocktail (pardon the pun) of small doses of a few of these compounds, injected locally, and held there for a few mins to encourage uptake, will enhance your chances of success with any extender or hanging you do.