This does require a bit of work and I imagine a few people do this already (I've done it for the past 2 years and I've just renewed onto my 3rd year) but just in case people don't realise it's possible I thought best to share.
1. Log onto your account and click on the "Upgrade to Pro" or "Renew now" option.
2. On the next screen, leave the page a few seconds then try to close it down - you will get a little pop up box - click "Cancel" on the pop up then click on the "Get for free" box.
3. Go through the offers and sign up for eMusic - you will need to download their "Music Downloader" and enter card details.
4. I canceled my 'subscription' without downloading a single song literally minutes after signing up. Got the confirmation email that I could upgrade to Photobucket Pro about 6 hours later. (It's very easy to cancel... everything is done through the website - takes about 4 clicks).
FYI - the emusic downloader is easy to get rid of. I uninstalled the program with no fuss whatsoever. No ad's, no surveys or anything.
Some of the other deals you can sign up for to get the free upgrade are ok but this is the only one I can find this year where you can get everything thing sorted all online without spending anything, making phonecalls or with any real hassle. Also, this is only applicable to new members only... but I'm sure if you use a different email/card details it will still go through.