Haven't seen this posted yet, but it may partially answer the question of whether or not HarperCollins will allow Harlequin to keep running discounts directly off their website and/or be couponable elsewhere, since they seem to be trying this instead:
Harlequin is now doing this My Rewards test program for their US customers wherein you earn points by shopping and sharing (presumably via social media) your HQN-imprint books from their site (ETA: apparently it also applies to titles you buy physically and elsewhere online, though I don't know how they'd really do proof-of-purchase for that; maybe they make you scan & submit your receipts?) and eventually build up enough to earn free books (or enter special contests, but I myself wouldn't bother since the books are a guaranteed return, unlike the contest prizes which strike me as a waste of perfectly good points).
I don't know if this is available to everyone, or they're just randomly sending out the emails to fill up their test quota, but I'm a no-romo who doesn't buy stuff from them and in Canada besides, so I can't make use of this and maybe you can.
Here's the linkage to sign up for the test program:
Harlequin My Rewards (must be a US resident, over 18, 1 account only, free ebooks are redeemed via a coupon with a cover value of $8.99 or less so pick the pricey ones on your wishlist, etc.).