echo >> 127.0.0.1 google.com C:\windows\sytem32\drivers\etc\hosts
That might work for you. I don't remember if the 'hosts' file is a text file or something else in Windows, though. Best thing to do is create a copy of your hosts file and test it on that first.
Out of interest, is there a reason you want to do this?
Edit: Whatever you do, don't miss out one of the less-than signs. If you were to do the following:
echo > 127.0.0.1 google.com C:\windows\sytem32\drivers\etc\hosts
It would add 127.0.0.1 google.com to the file, but would delete everything else in there first (assuming that it works at all).