You can use the system.importSystem command. When you pass it the computer name parameter add a backslash.
To test this out easily you can use the API explorer in the ePO Tools Exchange or use a browser with the follwing URL. Once authenticated you should see the new group.
Subgroups can be create by adding addtional groupnames with backslashes
API Explorer https://community.mcafee.com/docs/DOC-2931 :
Bumping an old thread to avoid duplicate posts. Has this been updated in ePO 5.1.2? I tried to call system.importSystem as follows but it just created an unmanaged system in the lost&found.
wget -q -O - --no-check-certificate --user=USERNAME --password=PASSWORD https://server:8443/remote/system.importSystem?names=testgroup\&branchNodeID=2
Any advice would be appreciated.