One of the many companies Aardman Animations (the studio behind Wallace & Gromit and Creature Comforts) have made adverts for is LEGO. What is uploaded on YouTube by the Hall of Advertising channel is one advert done for Train...

And one very impressive advert done for Pirates...

But also, my Creating 3-D Animation book mentions a spaceman advert Aardman made that was similar to the Pirates one. I looked it up and yes, I found a Space advert with the same construction characters (2:30):

But I've also seen listed in an interview a mention of producing advertising for LEGO Star Wars. This interview came out before Chicken Run and LEGO Star Wars came out in 1999 so it must have been in the franchises early years.

http://www.telepathy.co.uk/aardman/culture/faqs.html

Does anyone know of some early LEGO Star Wars advert with stop-motion in it?

Awesome! I'd seen some of these stop-motion adverts before but I had no idea they were actually produced by Aardman Animations!

Long time since this topic has been updated but might as well share this commercial that I think was the LEGO Star Wars one they were referring to:

(Alt version)