From the All Updates view, enable the Downloaded Count column, select the updates with Downloaded Count > 0.
Run the Update Management tool and configure the "Install Only" option for those selected updates.
On the Computer Selection dialog, target the task to the WSUS Server "All Computers" group.
The "Install Only" option requires that the content is already downloaded. If the content is not downloaded, a machine will generate a task error for that update, but will not be able to install it. If the content is already downloaded, the update will be installed.