Update custom field when updating role?

First of all I set global look up keys in Config --> Global Lookup Keys:

test --> 1234

When I call GET /system/config I get the following answer:

“lookup_keys”: [
{
“name”: “test”,
“value”: “1234”,
“private”: false,
“id”: null,
“role_id”: null,
“user_id”: null,
“allow_user_update”: null
}

If I set Lookup Keys on User or Role I’m not able to receive the values through API.

I could solve this problem with a “dummy table” like [in this post][1] but it’s not a very elegant solution.

Do I have an error in reasoning with the use of Lookup Keys or isn’t there really a possibility to read out non-private Lookup Keys through API?
[1]: Lookup Key not being Inserted for callStoredFuncWithParams()