Near-field-communication / NFC at no cost
Apologies if you have already, but have you considered using IR to communicate? It solves both the low cost and connector issue, whilst being reliable and simple to set up. Such an LED could be hidden in plain sight, behind a translucent bezel around the LCD - should it have one. 

Sparkfun have a great intro to Infrared communications - it may be a bit below your level but contains helpful info anyway.