TrueType hinting: hint from, but not align to, baseline – how to?

How can I apply such instructions, when there is no origin point in Glyphs? The comma should be tied to, yet there is no point that should align to, the baseline. To acheive this, I would use two stem hints in FLS: The first defines the distance from baseline to the top of the comma – the second from the top of the comma to the bottom.

You can align an anker with a zone. That can be used for accents, too.

There is nothing to attach an anchor to. Am I missing something? Right clicking on the zone gives no options for placing an anchor. Pressing A when hovering over it does not work either.

Add an anchor to any node. Then select the zone you what to attache it to from the info box.

What is supposed to be the effect? It doesn’t change the alignment.

Aligning to the baseline does not change much as the baseline is not effected by rounding.