You could shut down the 7-mode controllers and swap disks between shelves so that one shelf has the disks owned by controller 1 and the other shelf has the disks owned by controller 2, then restarting the systems. This would require an outage but would be quicker than moving disks while the systems are running.
Definitely in the "painful and slow" category, you could do what you're talking about by converting data disks to hot spares (one each from each aggregate - allowing time to level), remove ownership, eject, swap, own as hot spares on the opposite node. Rinse, wash, repeat. If these are big SATA disks you might be looking at a pretty long process.
At a high level, you'd just need the 7mode equivalents of the following commands: