Setting a user as an administrator via drush command line?
drush help user-add-role
Add a role to the specified user accounts.

Examples:
 drush user-add-role "power user" 5,user3  Add the "power user" role to the accounts with name, id, or email 5 or user3, uids 2 
 --uid=2,3 --name=someguy,somegal          and 3, names someguy and somegal, and email address of billgates@microsoft.com       
 --mail=billgates@microsoft.com

Arguments:
 role                                      The name of the role to add                                                
 users                                     (optional) A comma delimited list of uids, user names, or email addresses.

Options:
 --mail=&lt;me@example.com&gt;                   A comma delimited list of user mail addresses of users to operate on. 
 --name=&lt;foo&gt;                              A comma delimited list of user names of users to operate on.          
 --uid=&lt;3,5&gt;                               A comma delimited list of uids of users to operate on.

Aliases: urol


So, for your use case:

drush user-add-role administrator USERNAME