det wrote: Is it possible to have the entry's main headword displayed instead?
Not really. For both GoldenDict and Lingvo the multiple headwords are equally significant, and there is no single *main* headword among them. In fact, Lingvo DSL compiler, before compressing the DSL into proprietary format, expands all cards with multiple headwords into multiple cards with single headword. After such transformation, each card has exactly one headword and knows nothing about others.
Yes, sometimes this is not the best approach and I've seen dictionaries that trying to deal with this one way or another. The most popular solution, it seems, is to put the main headword also in the card's body, on the first line, in bold. This is also easily scriptable in your case: find cards with multiple headwords, and copy first headword into first line that starts with space or TAB.