From Colemak

The AutoHotKey script (AutoHotKey\QWERTY to Colemak.ahk) included in the Windows download allows trying out the layout without administrative privileges. This can be useful as part of your USB portable apps collection.

For the AutoHotKey script to work you have to make sure that the QWERTY layout is installed, that is set as the default layout, and that it is set as the current layout, otherwise some of the key mappings will be wrong.

This is mainly useful for those who don't have privileges to install a new layout This method doesn't support the multilingual features of the Colemak layout, and might behave erratically sometimes.

AutoHotKey home page