I would be really surprised if they let you do this, esp since it is already out of the store inventory. The only hope you have is if you have an SA there who is already your good friend, and even then, I would be very very surprised if they let you return and re-buy with the coupon.
I had a similar situation with ELuxury once, where I bought an Marc by MJ bag there, and then about a month later, it went on sale for nearly half off. I asked them for a price adjustment, and they said no, because it had been over 14 days since I had bought it. But since you can still return within 60 days, I asked if I could return it and then re-buy it at the lower price. The SA on the phone got really quiet and then said, very nastily, "I suppose so." Heh. But what I actually ended up doing was 1) returning it (because I was so annoyed at it being cheaper so soon after buying it from them) and then 2) finding it at NM.com for even less $ than the ELux markdown price. Yay! I'm convinced it was handbag karma rewarding me for not doing the return/re-buy, even though technically I could have.