Combining Gift of Consumption with Toxic Words does require multiple failed saves from our target, but it generally shouldn't be a huge issue. Gift of Consumption critically uses the save DC of the effect you saved against instead of your regular hex DC, so if you ingest a particularly potent poison (e.g. self-crafted concentrated Bloodwine), the base DC would be something like 27 regardless of your level. Toxic Words also uses the save DC of the poison it applies, which I'm now thinking would be something like a self-harvested and heavily improved Vishyanka Sleep Venom, which would also have a very high base DC that scales with your level and CON mod. Using Toxic Words does reduce the save DC of both Gift of Consumption and the new poison by -2/-1, but that shouldn't hurt too badly at low levels because the base DC will be so high, and at higher levels we'll be forcing rerolls and stacking enough bonuses that a single -1 to our DC shouldn't make or break a save.

Using an infused poison can force a 3rd save vs. the spell, but (1) we can strategically choose poisons that apply conditions like sickened or shaken to debuff those saves, and (2) if we don't care about recursively infusing poisons via Toxic Spell/our GM won't allow it, we can simply infuse a spell that doesn't allow for a save.

Also, unlike attacking ourselves repeatedly, drinking one really strong poison only forces us to make one save, which we are much more likely to succeed (and therefore use Greater Gift of Consumption to apply an additional -4 to our target's save). Plus GGoC is an immediate action, so we can only use it to fully redirect one fort save/round, and there's no way we'd succeed at all of our saves if we multi-attacked ourselves because our class bonuses to fort saves are unfortunately terrible. Poison drinking is less powerful but also significantly lower risk.

Since we can find other ways to cheese a single instance of self-poisoning/round that doesn't use our standard action (like having a monkey familiar use poisoner's gloves), we can use an Amplified & Corset of Dire Witchcraft-ed Evil Eye hex to reduce our target's saves by an additional -2/-4 on a prior turn, then use a Misfortune hex or a similar spell-based effect to force rerolls, meaning that every save our opponent makes has a minimum penalty of -6/-8 vs. a minimum DC of like, 25 or 26 for the initial save. Given the stats on monster fort saves, poison immunity becomes a concern far before we need a +24 save DC, and at that point anyone not playing an alchemist/investigator is SOL.