I understand it to just mean that he shrugs. The "tossing in" part means that he casually throws this gesture into his conversation. I agree that shuffling one's feet doesn't seem like a particularly cool thing to do, but remember that he's only a kid, and also that he's only "having a stab".
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.