Disclaimer: This is (once more) a post about the tool I wrote for this actual purpose. So yes, this is self-promotional...kind of. Well, not kind of actually, it is self-promotional...sorry. As further full disclosure, I do not know of any other launchers which can do that, only of the workaround I'll post in the next few seconds.
If you can live with the limitation that you won't be able to login at Mojang (and so can't play on servers which demand authentication) you can use the EasyMineLauncher. It is a simple replacement for the official launcher which grants you all kinds of options, but the important one for you is to change the home directory.
You can do it like this:
java -jar -Xmx1024M -Xms1024M EasyMineLauncher.jar --parent-dir=/path/to/your/new/dir/
Additionally, the launcher will give you some further options:
- The directory of the jars
- The minecraft.jar directly (which allows renaming of said jar)
- The directory of lwjgl
- The directory of the lwjgl native files
- The directory of the
.minecraft directory (by default
- A username
- Some window options
- A server and port to directly connect to
For further information please see the README.