Ishan,
The raw module works pretty much the same on Windows as it does on Linux - anything you can run on the command line can be run using the raw module. So, if you are wanting to use this nssm.exe rather than actually installing nssm, you would simply specify the path to the executable and pass whatever arguments it enables.
I haven't found a way to specify the AppDirectory upon creation of the service, so what I do is run the raw module to set that after the service has been created. For you, this might look something like this:
raw: C:\path\to\nssm.exe set [ServiceName] AppDirectory C:\path\to\appdirectory
Hope this helps.
-Joe