OpenVPN using IPv6 on VPS

I'm trying to create an IPv6 tunnel using OpenVPN on Debian Sid. IPv4 is working fine, but I can't get IPv6 to work. I can ping the server and other clients using IPv6, but I can't reach the internet from a client.

I've done hours of research but I still don't understand IPv6 completely, so this problem may be something really easy to fix. Some explanation would be nice!

The problem is that I'm using a VPS and I only have one /64 subnet for everything:

2a00:a123:4:b5::/64

So I thought I could add this to my OpenVPN config (create a smaller /112 subnet for OpenVPN):

server-ipv6 2a00:a123:4:b5::80/112
push "route-ipv6 2000::/3"

Now when I run ifconfig tun0 I get:

inet6 addr: 2a00:d880:6:f2::81/112 Scope:Global

And my clients get:

client1,10.8.0.2,2a00:d880:6:f2::1080
client2,10.8.0.3,2a00:d880:6:f2::1081

I added all these 4 IPs in the SolusVM CP (I don't know if this is necessary, I thought it would be for the routing back to the VPS). I also set net.ipv6.conf.all.forwarding to 1.

Still, I can't reach the internet over IPv6 from the clients. If I run traceroute6 google.com on a client I get to the server IP, but only timeouts after that.

I also found this similar question, but the NDP proxy thing doesn't seem to work for me using the following command:

ip neigh add proxy 2a00:d880:6:f2::1080 dev tun0
ip neigh add proxy 2a00:d880:6:f2::1081 dev tun0