preferably making each android appear unique
I don't think they all will be unique. I think that will be according to cost.
I am going to use sex dolls as an example. There's the real custom jobs, where you can chose all the features, and the price goes up the more customized you get. And there's the generic sex dolls, that, while expensive, aren't nearly so much. Therefore, I believe that it's far more likely that a company, like an airline or a Hooters-type restaurant, would have "base models," with 3-4 different types. It's sort of like the older Barbie dolls before they changed the actual features. The black Barbie used to look just like the white Barbie except dark-skinned, and Barbie's other friends looked JUST like her, except that they had different colored hair and skin tone.
This might even be a signature thing for a company. Airlines used to measure women's busts, waists, and hips, looking for specific measurements for their flight attendants. Sarah Airlines, where everyone is Sarah. Except for that actual human girl in Sacramento who Sarah is based off of. She gets residuals, but really hates to fly. And she's getting older, and the bots are not.
How can I justify the addition of these purely aesthetic human features on an android built for work?
For the service industry, or in places where a face matters, and the appearance of no expense spared, this is justified. But if you're talking manual labor? No, not really. There's not a reason to customize a construction worker.
Labor laws might say you are only allowed X number of 'droids, because otherwise, humans will be out of a job. Calculating the cost of employee benefits over time vs. just a workshop, unscrupulous employers started getting unauthorized "skins" for their bots to dodge the labor laws, perhaps even getting paperwork that says they are human. And perhaps the droids are even programed to believe that, which could be a plot in itself.