Having successfully negotiated for a steady supply of elf livers, my quest to become the ultimate dwarf can continue a little longer. However, the process of negotiation was not without complications. I won't bore you with the specific details; Suffice to say, I am now the custodian of a small number of elven prisoners.
Out of deference to my new elf-lord ally, I would prefer to treat these prisoners well. Knowing that elves, unlike dwarves, tend to pine away if denied sunlight, I have ordered that they are to get some healthy fresh air and exercise while working (strictly supervised) in my fields.
This decision has presented me with a question that must be answered. To the best of my knowledge, the Labour proficiency is required for a character to perform labour fruitfully. Unfortunately, these prisoners lack that particular general proficiency, having backgrounds as petty nobles and yeomen. As prisoners, they've no means to attain the campain or adventuring experience required to learn more proficiencies by levelling, and as adult elves, they can't gain further proficiencies as they age.
I therefore must ask: Is there any other way for humans and demihumans to gain the labour proficiency, so that they can be put to work? (Perhaps by swapping an existing proficiency for a new one?) And if there really is no way for them to gain the Labour proficiency, how much can I expect them to produce while labouring without it?