This works for me.
Make sure the magnet-link you give to your friend contains the tracker URL. Like:
magnet:?xt=urn:btih:abcd6nl56123kq6ebq2jxdsl7cylabcd&tr=http%3A%2F%2Fretracker.local%2Ftest
(not a real torrent)
1) Tixati Settings > Magnet-links > Magnet-link format (the default is this:)
magnet:?xt=urn:btih:[hash]&dn=[name]&xl=[bytes]&fc=[files]&tr=[tracker]
This will be the default for magnet-link copy
2) Select your transfer and go to its properties, iirc "Options" tab. Under "Metadata" there will be 4 different magnet-links to copy. Only the bottom two contain the tracker.
&tr=...trackerURL...