The servant glances at the hallway past you, a bit too anxiously. "She shouldn't be a minute. Would you like any refreshments?"
You've encountered this situation before, of course. Not being human, you aren't able to consume food or drink directly. You can incorporate such material, slowly working it into the enchantments and dampening fields that make up your disguise, giving the appearance that you are truly eating. Later, you can dispose of it somewhere private.
But such a display requires a great deal of concentration. Perhaps it would be best to decline. You have nearly reached your target, after all…