If they are on a single loop it will work. Or a thermostatic radiator valve. But one factor with MonoFlo tees is that they depend to a certain degree on the water that is diverted though the branch being returned to the main for use by the downstream radiators. If you shut off that branch you effectively reduce the amount of water being circulated. A three way valve, that either circulates through the baseboard or returns the water to the main would be a better option if the baseboard is going to be off for long periods of time.