[striplar]

I just found a link to the USB isolator I used.
http://www.ramelectronics.net/comput...prodM2100.html
there are two versions, I used the one that had a small power supply at one end ie a fibre-only connection.
Although this is expensive, it's the cheapest method I've found. Most of the others are hubs with 4 outlets which I guess is what makes them expensive.