You can use GHost++ with only one set of CD Keys by using the Admin Game. You then have to join this admin game via LAN, type a password, host a game, leave the admin game, join the created game and do everything you said before.
You can get all this at
Official GHost++ Home - Codelain.com - Index
Some people say it works for Garena in case you rename ghost.exe to
war3.exe and choose this file as the game executable in Garena settings, but I cannot ensure it works.
Nonetheless I recommend starting with LC before handling GHost++, as you have to config many things and GHost++ is quite difficult to deal with, really.