Configuring radvd between global ip and local subnet

[jonsmirl]

I have a Linux host which works on the global ipv6 net without problem using 192.88.99.1. The host has a USB adapter with an 802.15.4 radio in it. The 802.15.4 radio talks to a bunch motes also with 802.15.4 radios. These use 6lowpan/RPL to talk ipv6. The 6lowpan net is not directly visible to the host, the usb link implements the point-to-point SLIP protocol between the host and the 6lowpan net.

I've given the subnet the AAAA: prefix and I can ping all of the nodes in it. I can pass it in any prefix needed.
I can also ping global ipv6 addresses from the same machine.

So how do I give the motes behind the SLIP PTP link (tun0) globally visible IP addresses? All of my attempts so far have ended in failure. Turning on net.ipv6.conf.all.forwarding makes me lose global connectivity.