I understand that you want to keep alive some torrent files.
1.Add as many as trackers you can from searching on google and add them to your torrent in trackers section following guidelines.
2.There are usually seed boxes that are connected to almost every torrent file.They only activate if the request rate to the torrent is high.As the seed box ips handle other torrents too and are currently seeding it at speeds of 5mbps mostly or more .
3.To connect to these seed boxes you have to add trackers,Now even though they are added.They dont start downloading it from our ip.For this as i said the seed box ip needs a request.So i normally use another client qbittorent and copy magnet url right click fron utorrent and add it in qbitttorent to download in a different location different drive preferably. Now copy the peer list from utorrent and add them to qbitorrent.MAke sure you add ports too.
4.The seed boxes start downloading from our utorrent ip port and seed to ourselves but different port ip to qbitorrent.In the mean time seed boxes download themselves to 100%
5.These can seed at 5mbps to others who download the same torrent
THE IPs and port USUALLY START LIKE THIS: 10.240.254.anyno
THESE IPs can be added by trackers.THESE ARE COMMON PEERS WITH DIFFERENT PORTS TO ALMOST ALL TORRENTS.