Why would you need to run a torrent client in Sandboxie in the first place?
Only download trusted torrents with safe file extensions, if you download executable files then you can right click on them then run them in Sandboxie after they finish downloading. You can also upload the downloaded files to VirusTotal by using the right click extension.
Executable files will not automatically run especially if you have UAC enabled. The only chance of getting infected while running a torrent client would happen only if you manually run downloaded executable files, allow them to pass Windows digital file checker and approve them when prompted by UAC.
Thanks.