For the time being, I'm faking things in the texture itself by putting facial skin on a layer below the lips and doing a semi-transparent erase around the edges. It's an improvement, but the problem is that if you want a different shader on the lips than on the skin (usually, I'd say), you can see the difference.

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3