We can't get under the cap just waiving Salvador. You have three options, keep in mind Palmieri will probably replace Clarkson in a year.
1.) Trade a 1st with a decent prospect to get rid of Rolston's contract.
2.) Waive both Bryce Salvador and Danius Zubrus, keep them in the minors. This may solve the problem this year but Zubrus has two years after that and Salvador has another season.
3.) Trade Clarkson with Salvador and get a 3rd or 4th round out of it.
1) Waiving those two players are permanent solutions.
2) Clarkson + Salvador are definitely not just worth a 3rd or a 4th. I'd say a 1st to 2nd depending on draft position... Salvador is not that overpaid to drop Clarky's value so much and yes, I'd trade a late 1st, early 2nd for Clarkson any day of the week.
3) A more suitable draft proposal would be Clarkson + Rolston for a low pick (5th or 6th) or Clarkson + Zubrus for a mid pick.
You are getting rid of Clarkson while not even saying that much money.
And I'd rather have Clarkson than Zubrus, considering the age difference. Bigger picture, Clarkson is more important to this team.