I was going to modify a cable or adapter but ended up using the following:

Nikkai L16BT (available from Maplins in UK), see photo at bottom of post.

The adapter does not provide auto switching, to do this I then followed the "A Simple Method of setting the N8X0 with OS2008 to host mode - 'Extras' App" instructions in this link:

http://www.internettablettalk.com/wi..._using_OS_2008

The instructions provides "USB Host" and "USB otg" menus as shown in second photo.

I think this provides an easy way to switch modes without the need to modify cables etc.