I've looked through the options on KTorrent and I'm not sure this is possible. I'm wondering whether I can stop the queue manager starting any new downloads before the previously downloaded ones have seeded to a certain ratio? I use to use Azureus and I know it was the default behaviour on there. There only seems to be options for setting the maximum share ratio and the amount of downloads and seeds on this though, so I'm wondering whether I have missed an option or it's just not possible.

That's currently not possible