yes, I always intended for TaskChain to be able to do at least what QuizPort can do, and that includes adding the "Source file" as a URL.
One way to do this is to add a repository that already handles URLs, such as the DropBox or GoogleDrive repositories. Once those repository type are enabled for your Moodle site, you can add your HotPot/TaskChain source files straight from your DropBox or GoogleDrive account.
I can see that adding a HotPot / TaskChain source file as a simple URL would also be useful for some teachers - especially those such as yourself who already have a external store of Hot Potatoes files on a server somewhere.
It seems to me this could be done as either a new "URL" repository type, or by adding a new URL field on the input forms which looks and acts like the field on the "URL Resource" form. I don't think I have time to do it this year, but early in 2014 seems possible. It would probably be somewhere between 2-4 days work for me.