Just nitpicking here, but: If I correctly understand the code (can't currently check this ingame, wrong computer...), the amount of bonus drops is always given as "(0 - 3)". The Thaumcraft API states that other values are possible (see the documentation for addSmeltingBonus).

If I need to take a look at the decompiled thaumcraft code to write the liquid death integration anyways, I can check out how the number of bonus drops is calculated and see whether the plugin can easily give the correct numbers.

Looks like Thaumcraft takes the itemtstack added as a bonus via the API, then increases the count either up to one time (no bellows) or up to the number of bellows (at least one bellow). So the amount of bonus drops varies from bonusstack.count - bonusstack.count + 3. Since you already access the bonus itemstack anyways, this is just a matter of displaying the correct amount per recipe. Which I unfortunately don't know how to do, so no pull request for that from me - sorry.

Relevant part of Thaumcraft's source is in TileInfernalFurnace.ejectItem.