If the Celtics want to have a huge tax bill, they could get Lillard without sending the Blazers all that much salary:
To Portland:
Marcus Smart
Robert Williams
Many 1st round picks
Draft rights to someone who's never coming to the NBA (Giorgos Printezis in this example)
To San Antonio (or any other team with cap space, but this seems like a Spurs signing to me):
Evan Fournier via S&T for at least $13.4 million in year 1
2nd round pick for helping
To Celtics:
Damien Lillard
Derrick Jones Jr.
In this trade, the Celtics can use Fournier's outgoing salary to a different team to help aggregate with Smart to match with Lillard. This move saves the Blazers $31 million this year with the inclusion of Jones, who fits into the rest of the Hayward TPE. Portland gets no bad salary, and actually rids themselves of bad salary. They get a huge trade exception if they want to go that route (Jones can match with Smart for their side of the deal, meaning they'd get a TPE of nearly $36 million for the difference between Lillard and Time Lord.) The financial benefits of the deal hopefully make up for the good but not great draft compensation.