beware that CAD doesn't accept frozen ATPL, and on your conversion, you might get downgraded back to CPL (depending on FT).
IMO, SO is good only for the company.. not for the pilot. (no actual flight time experience at a very critical stage - you just learned how to fly and you'll spend the next 4 years or so... not flying).
As Kathey said, if you already have an ATPL, it means you already have a minimum of 1500h and you're probably a senior F/O somewhere. Aviation is all about upgrading, not downgrading.