Ability to create LLD item prototype of type "dependent" with a master item NOT only item prototype

The new dependent item functionality is awesome, but I would like an extension to make full use of it.
If I try to create a low level discovery item prototype of type "Dependent" I can only chose a master item from the list of item prototypes of the Low Level discovery rule, I would like to chose a master item that is defined on the host or template level.

Example of case scenario I have in mind:

Host level:
a) SQL query that returns an XML/JSON/CSV with many nodes in a single row/column

LLD level:
b) SQL query (used as LLD rule thanks to "db.odbc.discovery") that returns the list of nodes

c) Dependent item prototype, with master item set to the host level query (a) but with post-processing searching for a specific node (b) that extracts the value for the specific node.

in this way it would be possible to limit the number of queries to the database and also get the same value for all the nodes at the same time.