Answer
Any custom Lobby Element can be mapped to a form this way — it isn't limited to R&D-created elements. The configuration is done from the FORM itself, not from within the Lobby Element Designer: on the target form, enable 'Lobby' in the Context Pane at the bottom of the screen (RMB > Customize > Add Lobby to list), unlock the context pane to enter configuration mode, select the specific Lobby Element you want from the list shown there, and click the cogwheel icon to map the form's own fields to that element's parameters/values. This form-side Context Pane mapping is a separate mechanism from configuring click-through Navigation inside the Element Designer itself, and works the same way regardless of who originally built the Lobby Element.