The question you should be asking is not if you can get away with not using A (which by the way realistically is a strong no unless you change your left strafe to another key), but if you can get away with using CAPS.. the answer is no. Change to SHIFT or CTRL to crouch. I use CTRL, but I'm sure most jumpers use SHIFT. It's possible to use CAPS, but you're making it so much harder on yourself for no reason. It's like saying it's possible to drive with a blindfold. Why would you?