So, as I understand: take out the fan, so you don't need (or probably want) the moving rear nozzle or the roll posts or their ducts. In UK terms that makes it land based? Install a massive generator powered by the fan take-off shaft. Install the big l@ser and ancilliary equipment in the hole.
I doubt you'd need to go to all that trouble. At 40% efficiency, a 100kw laser would need a 250kw power source. Those are already available on the 787. The accessory gear box on either the F-35 or F-15 engine would need to be modified to handle the torque loads and the engine installation would need to be modified to fit the bigger generator, but that would seem to be much more doable than modifying an F-35B's lift fan system. By comparison, 18,000 SHP equates to about 13.4mw which at 40% efficiency means about a 5.4mw laser. I don't think Lockheed is anywhere near to scaling their technology up to that kind of power level. They're still working to develop 60kw, about 2 orders of magnitude less power.