Did you ever find a solution? I am considering the same scenario, but it seems as if the jumpstart automatically assumes GUI as long as there is more then 384M RAM. Thanks.
If you are on Solaris 10 u5 (5/08) you might need the
service_profile=limited_net
in the sysidcfg just to prevent being asked. The absence of this setting is supposed to be business as usual for...