couldn't wait...JUST DID IT with 11x14 paper---
used 2 oz of developer (double the theoritical exhaustion for one sheet--one ounce should have have developed to full exhaustion)
WELL--it worked pretty good BUT...I got like wrinkle 'bag marks"...it looks like you need air in there to keep the plastic from "pinching" developer away from zones or from concentrating it---if a wrinkle develops in the plastic, then it tends to suck the developer up by capillary action and you get a wrinkle mark....
Also...if you got 2 sheets to develop....well you better have 2 bags....once it's wet good luck loading a sheet...and then you'll destroy it likely wiht water makrks that will look worse than the "bag marks"
but HEY...I'm pretty sure this can be workable if you get enough practice and learn 'how to do it"...I did get a couple of images out of it...ther'es work to be done here