The short answer is, yes you can run specific commands from one controller to steal disk ownership from the other controller.
However, you need to be VERY careful when doing this. First thing is to make sure you are reassigning ownership to the other partner's spare disks. If you steal ownership from a disk assigned to one of its aggregates (or even worst, the root aggregate) you could cause some real problems for yourself.
By default the systems come shipped with 3 disk aggregates on each controller. If you are saying 12 disks are assigned to each controller, you will need to identify which 3 disks are a part of the root aggregate and which 9 disks are spares. Unfortunately there is no way of knowing this unless you are logged into the other head. Although if you are really laze you could just perform a cf takeover, run partner, followed by aggr status -r, and finished off with cf giveback.
Once you have identified which disks you want to steal ownership of just run "disk remove_ownership <disk_name>" for each of the disks you want to steal ownership of. Once you have done that, run "disk assign all".
You need to be in advanced mode to run some of these command. If you don't know how to get into advanced mode, you probably shouldn't be doing this.
Note, you won't be able to assign all 24 disks to one controller. The other controller will need 2-3 disks minimum for its root volume.