By looking at this forum:
http://h30499.www3.hp.com/t5/Calculators/bd-p/bsc-408#.UJapyHaBzMF
I discovered that a partially functional release of the missing HP39GII connectivity kit is available for download at:
http://www.educalc.net/2336121.page
With the kit installed on my laptop I was able to update my firmware to a 4th of September 2012 version, which has many improvements over the buggy version that shipped with the calculator back in June.
My calculator is reluctant to shake hands with the lap top but pulling and reconnecting the USB cable eventually gets the link to come up.