The working directory of the Minecraft Launcher can be changed with the --workDir argument.

This mostly operates as intended; however, if there is no %appdata%\.minecraft folder, then one will be created. No files are put into this folder, it just creates one, and doesn't use it.

Also, the true affected version is 2.1.13508 according to the About screen, but Jira doesn't acknowledge that version exists yet, probably because it was just released yesterday.