Hello,
Time by time people came with similar requests for PXE.
The problem with Vagrant is its expect some OS and be able to ssh into the box. And the first nic will be NAT all the time.
So for Vagrant, if you add a private_network, or a public_network, it should do better for boot.
You may need to use VBoxManage to tell boot over PXE, etc.
My suggestion will be search on google groups for PXE to see past threads, and have a look at packer to create a VM. If you pass a non-bootable iso, it should go for PXE.
Other trick is on packer you have same access to VBoxManage, so any change you do, it should work.