Thanks for the example.
I have made a script to do what I believe you indicated.
DECLARE @cmd1 varchar(500), @cmd2 varchar(500), @cmd3 varchar(500)
SET @cmd1 = 'print ''[?]'''
SET @cmd2 = 'IF ''[?]'' NOT IN (''master'', ''model'', ''msdb'', ''tempdb'') alter authorization on database::[?] to [domain/login]'
SET @cmd3 = 'IF ''[?]'' NOT IN (''master'', ''model'', ''msdb'', ''tempdb'') exec sp_addrolemember ''db_owner'', [domain/login]'
EXEC sp_MSForEachDB @command1=@cmd1, @command2=@cmd2 , @command3=@cmd3
cmd2 puts the checkbox next to the database in the login properties screen.