You already have tried most of the standard methods?
Pinning right after showering when muscles are most relaxed.
Warming your oil by wrapping it in a hot damp cloth(microwaving a wet rag works good), or using a blow dryer, or setting it in hot water for a minute or two.
Massaging the area post injection for a good 5 minutes.
Working the muscle you just injected for a brief moment post injection.
Using a heating pad on injection site (especially before/during sleep).