Why not do:

alias go {
var %x $replace($1,-o,.org,-n,.net,-c,.com,-co,.co.uk)
run http://www. $+ $2- $+ %x
}

However, you would have to specify -c for something for .com this would allow you to open some more.
Prompted with: /go -c hawkee
Runs http://www.hawkee.com