For negation, why not copy English on this? A negative auxiliary verb analogous to "don't" transparently formed from an older negative particle, used in some TAM classes, with that same negative particle (let's say its ga to be concrete) used for negation in other TAM contexts?

Soŝna ɡás wek'né
Soŝna-NOM NEG.DO catch.fish
"Soshna doesn't catch fish"

Soŝna ga móch'í wek'né
Soŝna-NOM NEG want.to catch.fish
"Soshna doesn't want to catch fish"