The following may be of use to anyone that wants to build both their project and the server data file (littleFs) with one click and then have them both copied to a directory so they are together in one place.

1. In your project create a file called copyme.bat
2. Paste the following code into the copyme.bat file

@echo off
setlocal enableextensions EnableDelayedExpansion

set from=%1
set dest=%2
set name=%~n5
del %dest%%name%.bin

set mkspiffs=%3
set spiffsdir=%4
set /A spiffstart=%6%
set /A spiffend=%7
set spiffBlock=%8%

set /A spiffSize=spiffend-spiffstart

%mkspiffs%\mklittlefs -c %spiffsdir% -p 256 -b %spiffBlock% -s %spiffSize% %dest%%name%.spiffs.bin

copy %from% %dest%%name%.bin

 

3. Add the following line in your board.txt file

recipe.hooks.postbuild.1.pattern=cmd.exe /c {build.project_path}\copyme.bat {build.path}\{build.project_name}.bin {build.project_path}\php\bin\ {runtime.tools.mklittlefs.path} {build.project_path}\data {build.project_name} {build.spiffs_start} {build.spiffs_end} {build.spiffs_blocksize}
 

The highlighted text is the directory where you want the output files to be copied to. Change this for your needs.

At the end of the build the server data files will automatically be created with the correct settings from VM.
Unlike the 'Publish' button (which creates the data file and then uploads it) this does NOT upload the file.
I'm not sure if VM has an option to just build the data file without uploading it..

Hope this helps someone.