Found this promotion. Looks like it's been there for a while but hasn't been posted here. Took me less than 5 minutes to complete the signup and transfer the points to my Krisflyer account.
From 1 February 2019 to 31 March 2019, join Heathrow Rewards and receive 500 bonus KrisFlyer miles plus a chance to win up to 15,000 KrisFlyer miles. Join the loyalty programme that rewards you for almost everything you do at Heathrow; Heathrow Rewards. Become a member before 31 March and you will receive 500 bonus miles.
The extra points offer is only available to new members of the Heathrow Rewards programme who join using this link (https://rewards.heathrow.com/web/lhr/join-page?promotionCode...) or register their card and enter promotional code SQ2019 before 31 December 2019.
500 bonus miles will be awarded when member enrolls using the specified code before 31 December 2019. Only one offer per member. Offer cannot be used in conjunction with any other joining offer. Heathrow Rewards Terms and Conditions apply.
The full details can be found at https://www.singaporeair.com/en_UK/au/plan-travel/promotions... and selecting the Heathrow Rewards promotion. Please make sure to sign up using https://rewards.heathrow.com/web/lhr/join-page?promotionCode... and not the usual Heathrow Rewards sign up page.
Once you signup, you have to login to your Heathrow Rewards account and transfer the Heathrow Rewards points to airline miles (Krisflyer/Asia Miles/BA Avios/Emirates Skywards and a few other).