Printing on 6 3/4 envelopes with a Photosmart 7525 from Chromebook

I am printing to an HP Photosmart 7525 from an HP Chromebook 14, here is my issue:  I want to print onto 6 3/4 envelopes.  I was able to make a template with Google Docs but the printer says that the paper is the wrong size...  SWEET!! I can't change the paper size any where that I can find on the printer itself, and being that you don't actually install the printer driver onto a Chromebook but that you just print to it from the cloud, I can't change the paper size on the printer either.  is there ANY way around this??  Really wish that I could just load whatever size paper I want and the printer would print to it like the good old days...