Hi, Sebastian.
It was easy: For BPM Tomcat 7.4.0, running on Tomcat 8.0.24, i downloaded the suitable 64-bit-Tomcat-Distribution (8.0.30 worked fine for me) and dropped tomcat8.exe and service.bat in the bin-directory of the BPM-Tomcat (camunda-bpm-tomcat-7.4.0\server\apache-tomcat-8.0.24\bin). Running the service.bat like this
service.bat install CamundaService
installed me camunda bpm as a service (appearing as 'Apache Tomcat 8.0 CamundaService' in the windows service overview) on Windows 7 and Windows Server 2008 without problems.
Stefan