I know alot of people have plumbed a fountain into their return to cool the pool and have had great success. I chose to take a different route and purchased a standalone fountain that runs 24/7 in the middle of the pool. The pool never gets above 90 degrees during the day and every morning it's about 80 degrees. I live in Florida and the temps have been in the mid 90s and my pool gets sun all day. This is the one I purchased and it works really well:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0840867477
Just another option for you if you don't want to plumb your return.