Has anyone who is not a EEA citizen done this? I presume even if planning to drop the last segment, you would actually need to buy a refundable ticket from Europe back to the UK, otherwise BA is meant to deny boarding on the return?
It may be a good idea to buy these tickets through Amex Travel rather than directly from BA. You get charged in GBP at the IATA exchange rate, earn 4 MR per £ if you have the Gold charge card as it tends to give 2x travel bonus, and no need to lie about living in Ukraine (not sure if the fee applies for non-UK origin though)
Downsides are can't book WTP or different classes outbound and return, and potential difficulty with or additional charges for changes and refunds.