more live rock is always a good idea. target for 1-2 lbs per gallon for your tank. It will help to get rid of the nitrates to have more live rock. If you add the sand though, it will likely create an increase of ammonia, which you do not want. there is a reef booster packet you can buy at the LFS that has more bacteria in it that may help kick things up so you can add a coral by the end of the week. If you are dead set on getting a coral this week, add another 5-6 lbs of live rock, an emerald crab, some snails, a serpent star and do another 5 gallon water change on friday. let it sit overnight and get you a coral on saturday.
-Doc