50 mirror zpool - reducing to just one mirror

Got a zpool with live data that consists of 50 mirrored pairs of disks. For the sake of argument, lets say each mirror is 10Gb. So total for zpool is 500Gb.

We're planning to move this onto different storage and would rather not have 50 pairs again. Much better to just have one mirrored pair of 500Gb.

Whats best way to do this?

I was thinking:-

1. Is there any way to nest mirror in a zpool? i.e. at the top level mirror the initial logical 500Gb with a new 500Gb disk?

Or

2. Extend the existing zpool by adding a new 500Gb disk. Then remove the 50 mirrored disks one by one. The zpool will retrain integrity and you'll end up with all data on the new disk and a zpool with just one 500Gb disk.