Enable verbose upload in settings. Set the IDE to the programmer/board/etc that you're planning to upload to. Try to upload any sketch (you don't need any hardware connected). In the black console window, there will be a line with the full avrdude command (with full paths for everything) at the top of the uploading section. Copy this into notepad, edit the path of the hex file to point to what you want, and then open a command window (cmd) and paste it in.