I think a living plant is and excellent idea if they have somewhere to put it. Try a garden center to get a heather, although I'm not sure it's the right "season" at the moment. Most centers sell small potted flowering perennials, many of which are reminiscent to buttercups. You could then buy a nice pot to match their tastes.
Some yellow poppies are reminiscent of buttercups, but they are big, so maybe back to the florist/flower shop for those. In my experience over here, the more unusual flowers from the florist don't seem to last as long once you get them home.
Otherwise, MASHfreak's suggestion of picking something yourself is cool -but then put them in a nice vase that reflects their taste.
Sorry, fresh, but I think white roses just don't fit the requirements outlined. None of the bog-standard formal stuff does. And mush can frighten off as many girls as it attracts. We're not all as dumb as you seem to think. And I didn't see grant mentioning it was a girl......
