Haven't used soulseek in about a decade, so things might have changed, but back then my workaround was this: I search for what I want, find a person who's sharing it, and if their library was good I'd allow them to see my library before downloading from them.
So basically I'd share with folks I downloaded from, but not the general public. Not foolproof, but drastically reduced chance that somebody with a well-curated library was there just to prosecute.
True. Now I pay for VPN with port forwarding, so if I were to use soulseek again I'd just share. Back then I was in the same boat as OP and couldn't afford a VPN.