Do you have login scripts for your environment? just need a "if not exist" statement for the LANDesk Management program folder on the pc to determine whether it needs to be installed or not.
Or, you can set up a gpo to do the install & set that on a particular sub-folder of your computers group to drop those pc's into until the agent is installed, then pull them out & re-deploy the correct agent for that pc from LANDesk