You can use a clientsettings.cfg file to tell clients to use automatic relay selection at install time.
Wanted to point out that this is not possible (in the scenario in which the BigFix client cannot initially connect to and register with the root BigFix server, i.e. BigFix clients out in the Internet). The BigFix agent first needs to register with a relay in the deployment and gather the main actionsite of the deployment before it is able to begin operating using an automatic relay selection method. The reason for this is because the BigFix client only knows of the relays within the deployment from the relays.dat file that is within the main actionsite. So if the client does not have the relays.dat file because it has not gathered the main actionsite because it has not registered with a relay, then it cannot perform automatic relay selection.
The user will want to make the first method of selection the client performs to be manual selection and follow the instructions in this article: http://www-01.ibm.com/support/docview.wss?uid=swg21505838, with the following settings.
Note: I also had a question recently that asked what is the expected behavior of the BigFix client if the settings appear as:
The answer is that if
__RelaySelect_Automatic is set to a value of 1, then the BigFix client will not consider or use the
__RelayServer2 settings in any of its relay selection determinations, they become dead settings.