The easy way
For the moment, IP addresses have to be assigened via DHCP. Place your DHCP server in the same network as the VPS-es that need IP addresses.
Placing DHCP server in same network
When you use a bridge with a certain VLAN ID for interfaces with internet (you can configure the default interface used for internet here), place the VM with the DHCP server in the same network. Configure you DHCP server to hand out IP addresses in the correct range.