Shooting IGF pre-training has no benefit. The idea of shooting IGF-1 post training is that receptors are upregulated in the muscle just trained. It's easiest to just do it when you get home, if it's not too long of a wait.
It would be hard to inject IM in your car, but I've done it in a bathroom stall at work. During the winter months, it's easy to make a pre-load of IGF & store in your car with your BW. I would train at lunch, then get my IGF ready in the car, & shoot in a stall before going back to work.
With slin, it's easy to shoot sub-q in the car or a stall at the gym. They sell little cases at pharmacies to store pre-loaded slin pins, designed for diabetics. You could obviously use for IGF too.