I use this Windows command batch script in my special built FPC setup:
@echo off
::#coding:OEM_850
set CURDIR=%~dp0
set BIN_TARGET=bin\i386-win32\
"%CURDIR%%BIN_TARGET%fpcmkcfg.exe" -o "%CURDIR%%BIN_TARGET%fpc.cfg" -d basepath="%CURDIR:~,-1%"
Copy and paste it to new text file, change its extension to .cmd and save it into your root of FPC directory (you should see bin subdirectory). Then execute it.
That excerpt makes your FPC installation portable one. Copy/move your FPC somewhere in your hard disk and execute that script to set it up.