Can't see how there'd be a problem getting a blue slip for that, should be sweet mate as long as your mechanic isn't an asshole. I wouldn't be too worried, could have been worse. At least they didn't give you any EPA or Noise related hassles.
Worst case scenario just bolt up a standard cooler, if you don't have one handy I'm sure there's plentyof people on here willing to lend you one. But from what I can see, it's a bullshit defect anyway, and you shouldn't need to change anything for a mechanic to pass it. I very much doubt they'd see that as defective or unsafe.