Splitter for the Rondo trade exception and 45 and another 2nd would work. Splitter makes about $9 million a year for 2 more years so would be cheaper than Robin Lopez or Biyombo on the free agent market, has playoff experience. I think he would be a good complement to Zeller either starting over him or backing him up. Im assuming the Spurs are trading him to go after LA, but I have not read the article being mentioned so this would open up more cap space for them.
I would trade Wallace and 45 and another 2nd rounder or two for Hibbert. It saves them $4.7 million and Hibbert's value is at an all time low and is an unrestricted free agent after this season so the Celtics would be getting Hibbert for essentially nothing and if he contributes great, if not then he is gone after the season anyways.
The Celtics need a rim protector and both of these are better options to me then moving up for WCS. I would move up for Winslow, Stanley Johnson, and either of the Euro's but not WCS.