Hi Dan
The only way to program the KL25 is via SWD. Just copy the header connector circuit from the FRDM-KL25Z board:

You can get a P&E or Segger programmer (these are typically used or some other low cost ones that can do SWD mode). The P&E and Segger JLink will work with the NXP tools (like KDS) which can be used for programming too. The programmers are often also delivered with dedicated programming SW which may be more productive too.
If you are a zero budget company or hobbyist with free time you can also use an existing freedom board to connect to your board and use its OpenSDA debugger to program. See Eric's blog for this:
https://mcuoneclipse.com/2013/04/21/using-the-freedom-board-as-jtag-programmer/
Regards
Mark