NSIS: Nullsoft Scriptable Install System

You can use the following command line switches (from NSIS FAQ) to customize your installation:

• /NCRC disables the CRC check, unless CRCCheck force was used in the script.
• /S runs the installer or uninstaller silently.
• /D=(Path) sets the default installation directory ($INSTDIR), overriding InstallDir and InstallDirRegKey. It must be the last parameter used in the command line and must not contain any quotes, even if the path contains spaces. Only absolute paths are supported.

If command line options don't work, they are most likely disabled by the author of the installer.