This is old but I have a solution that might help:
Instead of Quagga (which is old and shouldn't be used), this applies to FRR (the modern replacement).
Configured via vtysh or /etc/frr/frr.conf:
router bgp <<YOURAS>>
bgp router-id <<SOURCE_HOST_IP>>
no bgp ebgp-requires-policy
neighbor 169.254.169.254 remote-as 64515
neighbor 169.254.169.254 password <<YOUR_BGP_PASSWORD>>
neighbor 169.254.169.254 ebgp-multihop 2
address-family ipv4 unicast
neighbor 169.254.169.254 soft-reconfiguration inbound
Add the floating IP to a dummy or loopback interface.