if you already have the member created that you want as an admin, just run the stored procedure 

dbo.aspnet_UsersInRoles_AddUsersToRoles. 

DECLARE @return_value int


EXEC @return_value = [dbo].[aspnet_UsersInRoles_AddUsersToRoles]
		@ApplicationName = N'YOURAPPLICATIONNAME',
		@UserNames = N'USERNAME',
		@RoleNames = N'ROLENAME',
		@CurrentTimeUtc = N'CURRENTDATE'


SELECT 'Return Value' = @return_value

hope that helps