What I've done is a little perl script which uses traceroute to check changes to my external IP (noobish , but it isn't dependant on 3rdparty webservices).
If changed , I update my own "NoIP" page - I wonder whether my Freehoster or my ISP will register the abuse first.
So sharing files - you could use any webserver available.
I'm guessing you're trying it from a network you are not administering ?
Well , perhaps they block incoming HTTP requests - and how would you forward the port to your machine ?
I don't think there is a way for you then.
A little more detail would help.
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