When escaping with wheatly, you will come across children potato presentations for bring your daughter to work day, one of them has become greatly overgrown. If you look at the presentation that the overgrown potato is on, you can see "by Chell"
http://youtu.be/2P4mcSgozu0
In chapter 3 test chamber 17 (I think) you can find one of Doug Rattmanns Dens, if you get close to the wall with his drawing, you can barely hear Doug Rattmann ranting, it's hard to hear and understand, but one line you can most likely make out is "It's gone sir! It's been stolen! The ship is stolen!" which could possibly be referencing the Borealis.
http://i1.theportalwiki.net/img/8/8d/Dou...rug_r2.ogg
In some test chambers before you and wheatly escape, he will peek threw the walls and see you, it's possible to grab wheatly during this time, and bring him with you tell the end of the test chamber ( I haven't personally tested this)
http://youtu.be/0dk3nnLdBVw