We consider group key agreement (GKA) protocols, used by a group of peers to establish a shared secret key for multicast communications. There has been much previous work to improve the security, efficiency and scalability of such protocols. In our work, we describe secure schemes which utilize auxiliary channels in addition to that afforded by the open medium of radio. Such channels are often present in a human-centric pervasive ad-hoc networking scenario, though often neglected. We show that auxiliary channels can reduce public-key operations, reduce computational complexity, and strengthen security against an active adversary on the open channel, and against an eavesdropper on the auxiliary channels. Group key agreement protocols are usually often contextualized by their topology. We applied multi-channel schemes to different topologies, and found that the ideal topology may be different for different channels.