I don't know about Windows 7, but the SC and SrvAny utilities from the Windows Server 2003 resource kit still worked on Server 2008 the last time I checked; I've used this technique myself to get PDFCreator running as a service on our file/print box:
sc create NewService binPath= C:\Windows\System32\srvany.exe DisplayName= "My Custom Service".
(Those spaces between the equal sign and the value are actually required by SC. No, I don't know why either.)
Use Regedit to create a key called "Parameters" in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NewService\Parameters). Inside that key, create a string value called "Application" and enter the full path to the application you are wanting to run as a service.
Cross fingers, start service.