Limit BitTorrent client onboard QNAP NAS to download only

I have a QNAP TS-210 NAS device with Linux version of BitTorrent client embed into their native system. For legal reasons in my country, I'd like to become a "100% certified leech" and limit my client's upload to zero. Is there anyway I can do this?

So far, I've found out, that I can't use settings like Global maximum upload rate or Maximum upload rate per torrent to 0, because 0 means unlimited in case of my BitTorrent client. I've tried to enter values like 0.001 kB/s (which isn't perfect, but still better than nothing), but this value is rounded to 0, which -- effectively -- means unlimited again.

I've set Share Ratio to 0%, but it doesn't changed anything -- my client is still uploading (I don't know, if this is because bugs in it or if I'm changing wrong setting -- I'm total BitTorrent newbiew / ignorant).

Any help is apperciated.