There is an old script out there called "Wonder Shaper" which I use for this purpose; something is wrong with my DSL if I try and upload large files at the full bandwidth available; it causes a stall and dies (SCP/SFTP, etc.) so I have to limit the network stack for the whole laptop before uploading.
I use the v1.1a listed there on Fedora without any problems, for my 6mbit AT&T DSL I use:
...which "fixes" the problem at the slight cost of slow uploads. You can start/stop Wonder Shaper dynamically as well, it doesn't need to be enabled as a daemon or at boot time. This script should be exactly what you need.