The “proper” approach would be to call up the provider and ask for more; there is no reason to limit IPv6 assignments to end-users to just a single /64, and in fact the current best practices document (RFC 6177) recommends “giving home sites significantly more than a single /64”.

But what if changing the ways of your provider does not seem to be a feasible option, and you still want to have multiple physical networks with at least a semi-comfortable experience (i.e. not being forced to use DHCPv6 on every device, or bridge everything into one L2 LAN)?

This simple HOWTO explains how you can have one “primary” network with functional SLAAC, and an arbitrary (16 in my example) number of “secondary” networks, where only DHCPv6 will be available. Full two-way routing between all these networks will work without any issues.

Why bother trying to combine SLAAC and DHCPv6 networks, and not simply split the /64 into several smaller subnets and use DHCPv6 everywhere? Because I believe it is convenient to retain at least one network with SLAAC, I imagine this would be your main private LAN, where majority of your computers and other devices are, so that you can enjoy the convenience of SLAAC without needing to set up DHCPv6 clients on all of those.