Good question, I would've thought this would be possible, but perusing through the list of all the possible commands from:
http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_sw/v_63/cmdref/qref.htm
It doesn't appear that there is a command on the PIX that will allow you to do this. On the routers it's 'ip name-server'.
You could also try using the command lookup tool:
http://www.cisco.com/cgi-bin/Support/Cmdlookup/home.pl
The PIX doesn't support a whole lot of commands, so I just prefer using the first link to look for commands :)
Hope this helps!!!
-Denny