You are quite the Virgo Malibu. Now that I've gotten that out of the way...
It seems to me that the purpose for the ambiguity on your part is that Valentine's day has traditionally been a time to re-enforce whichever relationship you were in at the time. (Naturally if you weren't in a relationship, then you didn't celibrate, because what would there be to re-enforce?)
The current conundrum:
You feel like there should be some recognition of the Holiday, but you fear that anything you do might give the wrong impression, because at the moment you're convinced that you're fine with the status Quo.
I was going to make the suggestion of giving him a 'gift' the night before, but someone else beat me to it, and you've already said there aren't too many things you don't do already. I'll come back to this point later.
If what you want is to acknowledge the holiday (as I would think only proper given that you are in a relationship, no matter the severity, and even if you are seeing other guys, he is the only one you were planning to do anything for, am I correct?) perhaps some small token of your affection would be adequate to your purposes.
Roses are no good!, and DJ's pay attention to this, it might come in handy later when you're trying to establish which boundries you want to impose on your relationship.
You'd have to do a single flower, because if its in a bouquet, the emphasis tends to rest on the beauty of the arrangement, and not the message behind it, not to even mention the cliche factor. Red infers a passionate romance you yourself do not wish so scratch that as inappropriate. Yellow would infer friendship, another misconception, and white implies something that your sexual relationship already precludes... Orchids might be nice, but they're expensive and let's face it, unless he is a rare quality of man, the sentiment might be lost on him.
Resuming with the 'gift' idea, I'd have to say it's still viable, but its a bit tricky to pull off. Its viable because even if you're already doing everything (which I doubt. Had a dirty Sanchez lately? You never know exactly how freaky he is...) you can always do it a different way. Add a sensual massage, or a candle-lit bubble bath for the two of you. Then there are always various aspects of fantasy ready to be employed. The gift might be to fulfill one of his fantasies.
Example:
If he's got a hankering to play doctor, bring along a nurse outfit.
If he's always liked a stronger woman, leather would be appropriate, just a school-girl outfit would be if thats the way his pendulum swings. I hate to say it, but you might want to ask his buddies or sneak a peak at his porn collection to find out.
Honestly, what I would do is err on the side of simplicity. If you're spending the night and the morning with him (check) and presuming you don't have to be anywhere too important until later that day (it is a saturday, so perhaps check)... wrap yourself in a blanket and make love all night (start late if you have to), and then, in the afterthroes of your passion while you're still embracing, watch the sun come up with a mug or two of hot chocolate, and make a valentine's day wish on the sun just before it peaks over the horizon. (This would require you making the hot chocolate during one of your interludes, or before you begin, so be at the ready)
You say its common for you to spend the night, so no drastic change there. You can always return to whatever routine you might have afterwards and, if questioned, you could always say that you were simply enjoying the holiday.
Bottom line. Valentine's Day is a day for romance and you can get away with a bit more over this holiday than you could say, for St. Patrick's day. (my birthday by the way)
Who knows, you might enjoy the feeling of a committed relationship for a day without the committment that seems to frighten you so much. Then again, maybe then committment might not seem so scary. Either way you win.
Best of luck in life and love Malibu, and let us know how this one goes for you.
-CyranoDeBergerac