The Belgian Maritime Administration are offering STCW qualifications for commercial yachts which are a lot easier to achieve in terms of seatime and course length / cost.

However, we believe they are not currently accepted aboard British flagged vessels.

https://www.naviclass.com/en/cursus/stcw-officer-and-master-500gt/

(If you have any direct experience either of completing these courses, or of using these certificates aboard various flagged vessels, please contact webmaster@kingsfleet.org and let us know your experience, thanks.)