I have a post elsewhere on brokerage accounts. E*trade in HK can let you open an IRA account here in HK but what you can trade is limited (US and HK stock only).
The difficulty to invest for US expats in HK is well known and hence the earlier silence as serving British, Aussie in fact any other nationality in the world is far easier for the banks and more lucrative. Opening an account in the US without a US address is also a major pain due to local concerns with the Patriot Act.
If anyone is seeing Sarah Palin, please ask her to tell Sen Grassley to shut up and leave expats alone.
Hope this helps.
FTH