GTKY: Jess

How about... sending new ones randomly throughout the day while she's at work, in case the last ones lost their smell.
Better yet deliver them yourself, but don't just walk in there.. Disguise yourseslf as an older delivery man, get one of thoose vibrating things people have to use when their voicebox doesn't work & go on about how you lost your voice from throat cancer caused by smoking. Since women remember EVERYTHING you should probably go the whole 10 yards wearing gloves & all.

Tell her that you've been asked to recite the card by the sender personally (ought to be fun with that sound box...) & look at it while saying somthing from memory ending with "signed- NameHere", then place the card with the flowers & try to get out before she gets a chance to look at the card. In the card write "Don't tip the delivery man, he will be taken care of later. -NameHere"

See how many times you can pull this off before she starts asking questions about why the cards don't match what you said or she calls you, as the delivery man give outlandish excuses as many times as you can. If she calls you thanking you for the flowers or asking about the delivery man saying things not in the card insist that you never hired anyone to send flowers & if they come in again wait for them to read the card to see what they have to say this time, and call you right away.
Now go back but this time when you "read the card" do it without turning on the voicebox and actually read what's in the card this time, "It's time to take care of the delivery man."

Hopefully the reaction is really, really big eyes & an "i'm going to kill you" kiss, but there's probably some holes above that I have no reason to think through right now

Unless she is the boss it might be a good idea to plan this with them before hand, just in case she calls the cops on the delivery man.