So my advisor just informed me that I should try this in order to get 2 uw grades removed which would boost my gpa and look better on my transcript. These are classes from my former, unrelated major so I have no need to retake them. The process in my university includes submitting a brief explanation with any proof documents to a committee. I do not get to state my case in front of them.

I was hoping to get some ideas as to what to write because leaving school for poker probably wouldnt go over well. Does anybody have experience with this?

Retroactive withdrawal usually involves some medical condition and usually it's for the whole semester.

What jmark said. What documentation do you plan to show as proof of your inability to perform academically that semester? And as jmark indicated, no university will allow you to do a medical withdrawal from one class but not all of them. At least, I've never heard of one.