Accept not being a contender for a few years and rent out cap space to teams by trading for their bad contracts in exchange for picks and young players. And be willing to take on bad non-expiring contracts.
I agree that this is the right strategy, if you're going to rebuild.
So, what's the going rate for selling cap space? The Cavs got Kyrie Irving. We packaged two top-40 players, and took on a longer, worse contract, and we're getting substantially less than that.
If Danny insisted on a rebuild, he should have done the Cavs trade for the trade exception, and leveraged that to take on other teams' garbage in return for legit building blocks.
I really doubt Ainge has any interest in cap space. I think he's more concerned with breathing room between the salary cap and the tax apron. I honestly believe that Ainge will be looking for a quick reload via some sign and trade possibilities, or some trade deadline activities, particularly one where he'll be more focused on acquiring assets and talent rather than roster fit to contend this particular season.
I really have little worry about how he'll build our roster going forward. But personally, I don't want to play the salary cap game nor the draft game. I'm looking for Ainge to make some good trades until he finds an adequate combination, and I don't think we're that far off.
As is, we have some good young talent on cheap or manageable contracts. Green really came to his own last year, and he performed well in the playoffs, so that's a very good sign. Rondo and Bradley have shown to be a very very good combination and disruptive when playing together, and Sully is a lottery talent who just got his back fixed. You really don't want to waste too many years when you have this young core, you want to surround them with adequate talent as soon as possible, and there are some intriguing possibilities this particular year with some sign-and-trade opportunities... that's what I'm looking for at the moment.
PG-SG-SF-PF... that's 4 positions already filled with young talent, which includes an all-star and one of the best PGs in the league, and a top defender in his position for a SG.