This may help you: http://www.liquidstate.net/blog/technology/openstack-havana-home-lab-on-centos6-with-external-networking/
Basically, you need a virtual router to connect from you LAN to OpenStack private network.
I think, you don't need a Floating IP exactly on each instance. Only a virtual router, then you can create a static route on each machine in you LAN, for example:
ip route add 10.0.0.0/8 via 192.168.1.100 dev em1
Good Luck!