Best I could come up for Siakam for Boston is a multiple trade scenario
Siakam
for
White, Gallinari, Grant, Jackson, $$ (to cut Jackson), 25 1st (top 4), 27 1st (lotto)
2nd trade
Birch
for
2023 2nd (fit into Hernangomez TPE)
So post trade (with 3 open spots)
Guards - Smart, Brogdon, Pritchard
Wings - Tatum, Brown, Siakam, Hauser
Bigs - Rob, Horford, Birch, Griffin, Kornet
Then use the Richardson TPE to add someone in the 5.5 million range and still have the 2 spots for buy outs or veteran minimum type players.