Answered basically here -----> /t/4058/1
All you should do is intsall the app as normal, copy the installtion folder from where you installed it and put it on your usb drive no 'hack' needed. If you made settings then copy those too to your usb drive and put them inside the same folder there - try it
For running apps off your USB key with fine ease without having to go thorugh folders on your USB key I strongly recommend a small less than 1mb freeware called PStart from pegtop- get it that at the following link, I recommend it ------->>> http://www.pegtop.net/start/
btw - I am a big portables fan too 