We talked about it briefly either here on these boards or the official ones.
In order to get into SJG first semester, you're supposed to go in on August 1st and buy a summer pass as the reduced price for the last month. You can then go online and renew for the Fall semester and request a transfer to SJG. So for a little while, I had a MRG pass before I got transferred for the Fall semester.
You have a second chance once you renew for Spring semester, but I have no clue how many openings there will be at that time. Also note that those of us with SJG passes will basically have to pay for year round parking til we graduate, or we'll have to take a change on the transfer system again.
I thought someone was mentioning they were able to buy a SJG pass directly after the renewal period was over. If you weren't able to, it must have been a very small window for doing that.