You can change the install path by opening up impulse, clicking on the orb (upper left corner), and changing your folder preferences there.

Your mate can archive his installation (the location of the game files will also be found in the folder preferences, referenced above).  After transferring the file, you can "restore the archive" by clicking on the impulse orb (upper left corner) and click on "restore archive".

I believe the archive is tied to your account, so you can't use it but i'm not sure.

click the top left menu icon and click detect application. point it to where you placed the demigod install and it should verify you just fine and then patch.

You can also try this I did it during beta but guessing it still works...

Have your friend login to Impulse on your system.

Restore the archive (if the OS is the same).

Exit Impulse, relaunch impulse but login as yourself.

Click on the blue ? in the upper right hand corner and goto register a product with impulse. It will probably show Demigod with your friends Key. Select it, right click it, and pick  Remove Registration.

Then I forget... You might be able to just restart Impulse and have it update with the correct license key or you can put it in yourself if that doesn't work.

Good luck!