You can work the other way around; rather than specifying which nodes to use, with the effect that each job is allocated all the 7 nodes, specify which nodes not to use:
sbatch --exclude=myCluster[01-09] myScript.sh
and Slurm will never allocate more than 7 nodes to your jobs. Make sure though that the cluster configuration allows node sharing, and that your myScript.sh contains #SBATCH --ntasks=1 --cpu-per-task=n with n the number of threads of each job.