Common property cannot be assigned . It requires an exclusive use by law that is passes as a special resolution.
The OC can’t increase the unit entitlements to cover this as the lot property remains the same.
The OC could seek rent for the use of the land as the lot value is increased with the exclusive e use of the land and the pool
Alternatively the lot owner could purchase the common property from the OC.
There is no clear cut answer for you and I suggest discussions with a strata lawyer may find a suitable option.