Something like this will work:

A .bat file containing the following:

sqlcmd -S SERVERNAME\INSTANCENAME -E -d master -e -b -i d:\mssql\backup\backup_tlogs.sql -o d:\mssql\backup\backup_tlogs.log

Then in backup_tlogs.sql you would have:

DECLARE @name VARCHAR(50) -- database name

DECLARE @path VARCHAR(256) -- path for backup files

DECLARE @fileName VARCHAR(256) -- filename for backup

DECLARE @fileDate VARCHAR(20) -- used for file name

SET @path = 'D:\mssql\Backup\'

-- set up backup file suffix

SELECT @fileDate = datepart(dw,getdate()) -- day of week number 1 = Sun, 5 = Thu etc

DECLARE db_cursor CURSOR FOR

SELECT name

FROM master.sys.databases

WHERE recovery_model_desc != 'SIMPLE'

OPEN db_cursor

FETCH NEXT FROM db_cursor INTO @name

WHILE @@FETCH_STATUS = 0

BEGIN

SET @fileName = @path + @name + '_' + @fileDate + '.BAK'

BACKUP LOG @name TO DISK = @fileName WITH INIT

FETCH NEXT FROM db_cursor INTO @name

END

CLOSE db_cursor

DEALLOCATE db_cursor

This will keep 7 days worth of transaction logs; overwriting them as the week restarts. If you want to keep it for longer you'd want to play around with the date section of the filename.