I can confirm that the following OTG cable works without any mods on the N900:
http://cgi.ebay.com/ws/eBayISAPI.dll...K%3AMEWNX%3AIT
This particular bidding had ended, but I'm sure the item has been reposted (multiple times) already.

Funny fact is that the cable, despite being advertised so, shouldn't work on the N8, as the N8 got a square USB connector AFAIK.

Cable in action