Disspating the oil via blood pumping through the muscle is the only advantage possible to injecting the muscle beign trained pre-workout.
Blood levels of the hormone take 24hrs to peak anyway so there is no hormonal benefit.
And like mentioned, the effect is system wide, pinning your delts with Test Enanthate for example is not going to do anything to the muscle. The hormone makeds it to the blood and then becomes free hormone once metabolised. IGF and Synthol are the only times spot injections have a purpose.