Here's my favorite passive-aggressive I-don't-love-you-but-I-won't-say-so-because I'm-cowardly-and-want-to-keep-you-on-my-string-as-a-potential-booty-call trick: Don't contact the person at all in the week before Valentine's Day. This squelches raised expectations and prevents being talked or guilted into any Valentine plans. Then, contact late on Valentine's Day when all cards and roses are sold out and reservations anywhere are impossible, saying you're busy with something deeply domestic, and suggest meeting at their place during the week ahead. If the person happens to contact you in the week before Valentine's, do not respond. This also works for other holidays you do not want polluted by the presence of a person known to be lonely and potentially exploitable: Initiate contact only on January 2, or after midday Monday on a long weekend.
For added vicious cruelty, send a wordless crypto-e-Valentine on February 15: for example, a photo of a cute animal.
Congratulations on succeeding at fooling yourself that another human being is not a human being and that you have slyly crawled beneath their radar without their noticing -- without having uttered one single actual lie!