You can, but also remember, AD may have to waive his trade kicker, otherwise instead of 21.6M, you'll need 24M to match.
But that could still be accomplished I think.
For example, say Rozier agrees to go to Pelicans and they sign him around 3/48M (OR 4/64M) which is 16M AAV but 8M counts as outgoing (50% of salary) and between now and March, we sign an MLE player (from buyout market) to a 2-year deal.
Rozier (8M) + MLE Player (5.3M) + Tatum (7.8M) + Williams (2M) + Grizzlies Pick + 2-3 Future 1sts.
The players in the package puts us around 23M, but remember, if Kings Pick lands say, 13-14 spot (ideal scenario) then it counts as about 3M so we draft, sign draftee and then ship to Pelicans. Celtics pick may also be around 1M in value, and if Clippers Pick conveys it could be close to 2M in value. Otherwise, Clips pick could still be a solid pick that definitely conveys in 2020 if we assume LAC will land a star or two.
Those picks come into bigger value for us IF AD doesn't waive his trade kicker and we still need some salary to complete the deal. With that said though... if he doesn't waive the trade kicker, then it's probably a legitimate sign he's only a rental for us. Even Kyrie waived his for us, although he had 2 years left on his deal and salary-matching at that time wasn't a huge issue honestly.
It's going to require some coordination and creativity I imagine, but it's certainly possible.