I have a late 2011 Macbook Pro 8,1. What worked for me was indeed using a usb pendrive alongside the physical CD. I should also note that I used the 64-bit Mac image (http://cdimage.ubuntu.com/releases/11.10/release/) (edit: I read that you already are aware of it) (I honestly have no clue what the differences are, if it makes any.)
I created a live bootable usb drive using unetbootin from the ISO, then inserted the drive after Ubuntu booted from the CD to its menu. Press a key once that Human logo comes up, then insert the drive when the menu pops up.
After that, select to boot into the live desktop. It will fail to find the image on the disk, but will search the pendrive, and continue to load the desktop. From here, you should be able to install Ubuntu normally, although your woes of getting Ubuntu to work perfectly on the MBP are far from over :) (It is well worth the work, though!)