How can we use $flex$ syntax in Cloud value sets?

Our case is:

In Additional Person Info, we have 2 segments: the Value set in the upper segment has to be "Table" type due to our requirements. The lower segment needs to be dependent to the upper value but when creating a dependent value set, the system does not allow to select a table type value set as the independent value set of the dependent value set.

That's why we need to use a workaround to create table type value sets for both the upper and the lower segment and associate the lower to the upper by use of $FLEX$. It gives a syntax error so we need to have the corresponding use for cloud.