Link field showing rows of a child table of the current doctype

I’m trying to have a Link field that displays rows of a child table of the current doctype.
Let’s use BOM doctype as an example.
BOM has child tables BOM Item and BOM Operation.
Now let’s say that in BOM Item grid, I want to add a Link field to BOM Operation.
I use frm.set_query() to filter on parent so only BOM Operation of the current BOM are shown.
This is working well, but there is one major issue, the link field dropdown show only the hash name of the BOM Operation.

I tried to configure a title in BOM Operation but it seems it is not possible for a child table.

Has anyone done something similar, or have suggestion how to show meaningful name in the link field dropdown ?