/data/domains/windows/start_pci1.sh 0000:06.2.0
modprobe xen-pciback 'hide=(0000:06.2.0)'
xl pci-assignable-add 06.2.0
Binding 0000:06.2.0 to pciback
/data/domains/windows/start_pci1.sh: line 17: echo: write error: Invalid
/data/domains/windows/start_pci1.sh: line 18: echo: write error: No such
pci-assignable-add: malformed BDF specification “06.2.0"

That last error, and this page: http://wiki.xen.org/wiki/Bus:Device.Function_(BDF)_Notation  suggest that the parameter you pass into ‘xl pci-assignable-add' should be in the format “06:02.0” instead of “06.2.0”. The other errors might relate to poorly formatted PCI IDs as well: try ‘0000:06:02.0’ ? 

However, I have no idea if that’s relevant. Haven’t used xen in a long time...

I also found this link while browsing: http://wiki.xen.org/wiki/Bind_lib.bash_:_A_script_that_makes_pciback_with_modules_easier_to_use.   Might help?