Opt-in and trade. If he wanted to come here, and Cleveland wanted to accept CJ and Aminu (for example) as compensation.
Ehh, we wouldn't give up C.J, as in any chance LeBron would come here, C.J. would have to be here too.
I think it would work like this:
POR Gets: LeBron James, Kyle Korver (TPE),
CLE Gets: Maurice Harkless, Jake Layman, 2021 POR 1st, 2023 POR 1st, Right to Swap POR 2024 1sts.
3rd Team Gets: Evan Turner, Caleb Swanigan, 2019 POR 1st
Compared to letting him walk, Cleveland gains only $3M in salary in order to acquire 2-3 future 1sts and to swap Korver for the younger Harkless.
The 3rd team would have to value Swanigan.
A different version:
POR Gets: LeBron James, Miles Plumlee (TPE)
CLE Gets: Maurice Harkless, Caleb Swnaigan, 2019 POR 1st, 2021 POR 1st
ATL Gets: Meyers Leonard, Al-Farouq Aminu,
Could send Harkless to a team with cap space here if Cleveland doesn't want him.
Either way, you'd have a starting lineup of:
Lillard
McCollum
LeBron
Collins
Nurkic
And you'd fill out the bench with ring-chasing veterans who want to play with LeBron.