installing packages offline

[The Trystero]

very often, the terminal "fetching xxx" goes on forever.

Fetching ruby
--->  Attempting to fetch ruby-1.8.7-p174.tar.bz2 from
http://distfiles.macports.org/ruby


however, if i copy and paste the url into my web browser and download the
package from there, it takes a finite amount of time.

how do i get macports to recognize this downloaded file and use it instead
of trying to fetch a new one? with gems, i simply have to put it in the
current directory, but that seems not to work with port.