It's not the amount of gear that's causing the pain, it's what's in the gear that's causing the pain. If you inject half the amount, you'll still get pain. Perhaps you wont notice it as much since you barely injected anything in the muscle, but you still havent solved the problem. It's like saying, 100mg of poison kills me instantly, so I'll just to 20mg at a time so I can die little by little. The poison is still the same strength so you havent solved anything.
The only way to get around it is to cut the gear with something else.