In Settings > Agents/Plugins > Targeted agent settings You can set up throttling to limit how much bandwidth is being used. You can create seperate policies to manage clients, different groups of clients, and site servers. the only problem I have with this is the clients or site servers will still be transmitting the same amount of information, itll just be slower and more spread out.
The second thing I did for my WAN links, which seems to have had a greater affect, was to create a package server at each remote site. I designated regular workstations as site servers and only installed the package service. If the site already had a task and package server, the 2nd package server I marked as constrained. Constrained servers can only download from unconstratined servers and must be on the same site. One thing to keep in mind is when you upload/import a new image, it will try to push the image to all package servers. You'll have to go in to Settings > Disk Images and modify the package servers that will store the image. Package servers without task service cannot deploy images and the package will be marked as invalid on that system.
Limit your inventory policies to conserve bandwidth as well.