Just follow these steps:
Replace the following files (I used the default installation):

/root/fogproject/utils/FOGiPXE/buildipxe.sh /root/ipxe/src/config/usb.h

then fire:

/root/fogproject/utils/FOGiPXE/buildipxe.sh

and finally copy the files to the target folder:

cp -r /root/fogproject/packages/ftp/* /tftpboot