The only other way you can try is to join the British Armed Forces and apply for British Citizenship after 5 years' service -
東網透視:憑一支單簧管 香港仔入選御林軍
以香港第一人身份成爲英國御林軍樂手,
David憶述,源於幾年前一次聚餐時偶遇英國陸軍音樂總監,對方提起英國御林軍樂隊招募新隊員,他持有英國國民(海外)護照(BNO)身份也可參與招聘考試,故決定一試。軍樂隊考試分兩部分,體能為先,音樂第二。對於當年33歲的他來說,體能測試是極大的挑戰,要10分半鐘內跑完2.4公里,亦要做掌上壓及仰臥起坐,首輪面試因跑步不達標而失敗。但他並沒有放棄,返港苦操3、4個月後再接受挑戰,2013年過關斬將通過所有測試,成功取錄。
身為英皇室的御林軍,薪酬福利令人關注,David則不予透露,僅指薪金水平較香港警察低一些,除普通的醫療和交通福利外,最優厚是住房福利,他與同事在倫敦市中心合住一間800至900平方呎單位,月租只需30英鎊,僅相當於300港元,相信令不少香港青年人羨慕。
他現長居英國,還有一年便可入籍,目標是繼續在軍隊攀升,成爲終身職業。
http://hk.on.cc/hk/bkn/cnt/news/20170812/bkn-20170812093047180-0812_00822_001.html
Please note that members of the British Armed Forces are not subject to UK immigration control.
https://apply.army.mod.uk/how-to-join/can-i-join/nationality
WHEN YOU JOIN
You'll be given 'exempt immigration control' status while you're serving. This will stop when you're discharged - and you'll need to regularise your immigration status if you want to stay in the UK. You can only do this once you've left the Army, having served at least 4 years.