I’d send a very large taxidermized elephant. Beam it straight up to their mothership. When they claim that it’s not very cute, I’d provide a long-winded pseudo-philosophical diatribe about the meaning of cuteness and how they should not be so quick to pass judgement. While their council convenes to decide our fate, the world’s greatest covert operatives exit the elephant through a carefully concealed trapdoor in the bottom. They commandeer the ship. Let the counter-invasion begin.