In order to stop the service early in the installation you will need to add a WiseScript to the installation.
You will need to create a WiseScript that uses the Start\Stop Service action. In the name field, enter the Service name.
Then, place the WiseScript before the CostInitialize action in the Execute Immediate script, so that the installer knows it can pick up the file when the time comes. Costing is the area of the installation where Microsoft Windows Installer evaluates the current state of the machine to which it is installing.