cheatproxy is a HTTP proxy which intercepts communication with
BitTorrent trackers and modifies the amount of data uploaded. By default
it listens on localhost:8000 so it should simply be a case of running
cheatproxy and configuring your BitTorrent client accordingly.

cheatproxy uses a file to map BitTorrent trackers to a number which the
amount of uploaded data will be multiplied by.

By default cheatproxy will look for a file called "trackers" in the
current directory but you can use the -f command option to specify an
alternative. The "default" mapping will be used when no other is
applicable.

cheatproxy comes with a sample file called, unsurprisingly, "trackers"
which illustrates the syntax.