I have a private torrent that I partially downloaded. I downloaded about 20% of the torrent across several files. I'm not interested in this torrent anymore and don't want to waste ratio, so I stopped the download. Is there anyway to tell tixati to just seed the pieces I have without grabbing any new pieces? I know I can mark entire files as "Do not download"? But I basically have a bunch of random pieces in each file, and just want to seed that.

Set the incoming bandwidth/priority/etc to something ridiculously low. It should basically do what you need. I understand why Tixati won't allow you to set an outgoing bandwidth limit to 0kbs, but maybe it could be added for incoming as it wouldn't hurt anything.