Getting Parent Entity in Code

Situation

I have an entity (party) that is a child (parental relationship) to the matter entity.  I am a beginner at coding Javascript and now realize that when I am accessing the entity behind the party form, I am accessing the form contents and not necessarily all the fields for the entity. 

So, on the party form I can't get the ID of the parent matter unless I place the matter lookup field on the form.

Is there a way in code to obtain the parent MatterID without placing unneeded fields on the form?

Thanks,
Glen

P.S. - This is how it works IF the matterID field is somewhere on the form.

var sourceMatter = parent.Xrm.Page.ui.controls.get("matterID").getAttribute().getValue();