Where to write set JAVA_OPTS in setenv.bat for tomcat 7 windows installation

There are various similar questions but none answers where to embed the environment variable. Unfortunately, in my case there is already a file named setenv.bat which contains a lot of code.

There is a lot of code in it. So the question is where do I write (on which line at what place within setenv.bat)

set "JAVA_OPTS=%JAVA_OPTS% -Dblockchain.callbackUrl=http://example.com/"

I wrote it at the beginning of setenv.bat but it doesn't work.

FYI : I installed tomcat using the windows installer, hence, I have tomcat7w.exe

I'm running tomcat as a windows service

I'm trying to access this variable through Spring in my webapp as :

@Value("#{systemProperties['blockchain.callbackUrl']?:'http://localhost:8080/'}")
    private String callbackHost;

Update

I tried setting it in catalina.bat, still didn't worked.