Is it possible to call a batch file while compiling an Inno Setup script?

As an addendum to the accepted answer, here is the documentation for Exec() in case the help pages ever go down.

Inno Setup Preprocessor: Exec

Prototype
int Exec(str 1, str? 2, str? 3, int? 4, int? 5)

Description
Executes specified executable file.

First argument specifies the filename of the module to execute.

Second argument may be used to specify command line to execute.

Third argument may be used to specify the working directory of the process.

Fourth argument should be set to zero, if you don't wish to wait for the process to finish, and non-zero otherwise. By default, non-zero value is assumed.

Fifth argument can be any of the SW_* constants defined in ISPPBuiltins.iss file. For GUI processes, it specifies the default value the first time ShowWindow is called. By default, SW_SHOWNORMAL (i. e. 1) is assumed.

If fourth argument is omitted or is non-zero, the function returns the exit code of the process. Otherwise, the function result indicates whether the process has been successfully launched (non-zero for success).

If you have ISPP installed with Inno (It's built in now) then you can use the Exec() preprocessor function to run your batch file. The compile will be paused until it returns (place it at the beginning of your file).

#expr Exec("c:\file.bat")

If your command takes arguments, you have to write it as:

#expr Exec('c:\my_cmd.exe','some_argument') 

You can also run it from a batch file that then calls the setup compiler.