Hierarchy SUBNM prevent selection of > Level 1 elements

Hi,

We want to show C and N level hierarchies, but only allow the user to actually choose an N level element.

It is a similar idea to having a menu (which content comes from a dimension) with options (N levels) organized by group (C Levels).

Is there a way to do that currently or is it something you could think about?

Cheers,
Celine