How to enable ULVT cell only part of design in synthesis?

[Fun-King]

Hierarchy:
HARD_BLOCK
|- BLOCKA
|- BLOCKB
|- BLOCKC

How can we just use ULVT cell in BLOCKA during synthesis?

solution A: Treat BLOCKA as another hard block or soft block, do synthesis independently.
solution B: Constraint ULVT percentage as m during synthesis. m < (BLOCKA std cell number )/(HARD_BLOCK std cell number)

Is there any other good solution ?

 

[oratie]

Synopsys Fusion_Compiler has
set_target_library_subset -object objects
where objects are hierarchical cells in the current block