I'd add several, actually.
First, I'd resign Ray.
Second, I'd use Tony Allen in a sign and trade deal to acquire a future draft pick (preferably 1st round) or something. I would do this because 1) I hate Tony the Turnover and 2) because his value will never be higher than what it is right now (like Glen Davis last year).
Third, I'd find a way to acquire Greg Monroe (our center for the future). Although this will probably require us to part with Perk (and perhaps Glen Davis because of his expiring contract), I'd do that in a New York minute. Now I know that people will protest because of Perk's defense, but I just feel that, for the future, and as the Big Three get older, it's important that we have 5 offensive options on the floor at all times (plus, Monroe has better size and is a better athlete, so why couldn't he do just as good a defensive job (or better) on Howard and others as Perk?). I'd also start him at center next year, but that's just me.
Fourth, I'd purchase/acquire as many 1st round picks in this year's draft as possible, and hope that we can get Paul George, Lance Stephenson, and/or maybe Luke Babbitt, you know, a couple of future stars.
Finally, I'd look to plug in the remaining holes with veterans that, for the most part, have yet to taste the champagne. Personally, I wish that we had kept Stephon Marbury (and no, I didn't forget the vasoline incident) after last year so that we would have had a great backup for both Rondo and Ray (I love his passing and his ability to create for himself as well as others) - I think that going through a full training camp with us would have given us the player that we thought we were getting last year (it's really unfair to expect someone who was off for almost a whole year to come in and pick up right where he left off). I also know that he said that he will be coming back next year, so I'd sign him for a year or two and play him for 25-27 minutes a night. Additionally, I'd add Jerry Stackhouse as a backup for Ray and Paul, would at least consider retaining the services of Marquis Daniels (who was great for us before he got hurt), sign Roger Mason jr. and/or Raja Bell for shooting and defensive purposes, look into signing Ben Wallace for more offensive rebounding, and hey, while we're at it, why not somehow acquire Tayshaun Prince so that we'd have someone to guard Odom, Josh Smith, Dirk, Rashard Lewis (despite KG's job on him in this series) etc

.
Yeah, I know I'm crazy.
Starting lineup:
C - Greg Monroe
PF - KG
SF - PP
SG - RA
PG - RR
Bench:
Sheed, Stack, Marbury, Big Ben, Roger Mason/Raja Bell, Tayshaun Prince, Paul George/Luke Babbitt, other rookie(s).
We'd have the deepest, most flexible roster in the NBA. It's a shame none of this will ever happen, but this would be my dream team.