I think hwat you have suggested below is the safest bet… but remember there is more than one Google user agent too, see here for a start:
http://www.user-agents.org/- you can trawl thru manually, or use the search in top right of the site (obviously search for the word google) – THis search may not get em all tho! – there is an xml sheet in the top left, you can download and sort in excel maybe 
@HenrikG 216740 wrote:
Thanks for the input, after looking into the different solutions suggested from you and other affiliates and AM’s it has been decided that we will go with a solution that includes using the user-agent to see if it is a bot or not.
So hopefully the stats will be even better, with a more accurate hit stats within a weeks time.
Cheers
Henrik