Does Ubiquity support installing via PXE?
You need to export the live filesystem over NFS, and set the NETBOOT and NFSROOT kernel command line parameters.
See this help document (under "A variation") for the full details.
The trick is to load a minimal system with NFS-Support. This system can start the graphical installer. This hotwo should help setting this up.
If you like experimenting around with pxe I recommend fog, this has alot of features and will setup part of the installation by itself. It will also allow you to backup partitions over network and load them back.