Had similar thoughts, but looking at the ii website if you log in after hours, there is no obvious facility /menu option to either Buy/Sell GGP on the ASX though I'm sure it must exist.
Need to ask ii if this is possible?, thought GGP shares would have at least been classed as cross tradeable /Fungible?
I would have thought, that instead of going down the Pension Ombudsman route which I have also used successfully in the past unfortunately takes such a long time.
You could therefore ask, say ii or other provider, to simply transfer your Sipp to them , they do all the hard work and it would be a lot faster IMHO .