There are hundreds and thousands of idioms and if one start reading all those, I think, wouldn't be able to, in two months. I had a separate book for idioms but couldn't read even half of that for CE2013. Keep one thing in mind that idioms comprises only a tiny part of the paper and if you want to master it that would, obviously, be at the expense of other questions. So preparation of those idioms that have been given in the past papers is an agreeable option then.
Anyhow Good luck!

__________________
"Success is not final, failure is not fatal; it is the courage to continue that counts" (Winston Churchill)