Download file through Web Service???

[rtc]

I am trying to think up solutions for downloading files
through HTTPS to a third party server. I have researched
BITS and would really like to use that to manage the
download.

I was wondering if there was a way to access the file
through a web service rather than supplying the actual
url.

For example https://server/files/graphics/iso.zip is not
a problem but I would like to do something like
https://server/file.asmx?fileid={GUID}.

Is that even possible? BITS might not know how to
download the file but is it possible to even begin
downloading a file using the second url? Could someone
please send me down the correct path?

Thanks in advance.