you can pass the user agent string in the command line
for example, this is how to make chrome report itself as IE8.0 on my machine
C:\Users\XXXX\AppData\Local\Google\Chrome\Application\chrome.exe --user-agent="Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1) ; .NET CLR 3.5.30729)"
so basically just add --user-agent="what ever you want to impersonate to" to the target in the shortcut to chrome
and launch chrome using that shortcut!
Source: http://www.google.com/support/
