So it just sounds like you need a host entry on your guest machine pointing back your host machine?
You could do something like the following:
Vagrant.configure("2") do |config|
require 'socket'
local_ip = UDPSocket.open {|s| s.connect("64.233.187.99", 1); s.addr.last}
config.vm.provision "shell", inline: "echo \"#{local_ip} myapp.dev\" >> /etc/hosts"
end
This should use a socket to get your host machines IP address and then using a shell provisioner it will append that IP address to your hosts file which should allow your VM to use the domain name you want to communicate with your host OS.