Conditionally_filter: Derive filter value from DB

I was trying out conditional_filter to add a default filter and a couple of other filters that would override the default filter in case picked by the user. From the documentation it appears there is a definite set of filter expressions that can be applied to the conditional_filter. The problem here is, I need the value for the default filter to be set dynamically based on a field from a table in DB.
Is it possible to add sql to conditional_filter for this use case? If not, is there an alternate solution that caters to this use case?

The first thing my brain jumps to would be replicating the conditional logic that’s conveniently created for you by the conditionally_filter, in a sql_always_where parameter.

You’d have to spell it out yourself, with

{% if view.field._is_filtered OR view.other_field._is_filtered %}
1=1
{% else %}
default filter logic, you can reference anything dynamic in the SQL here.
{% endif %} 

Which says pretty much the same thing as

  conditionally_filter: {
    filters: {
      field: field_name
      value: "Looker filter expression"
    }
    unless: [field, other_field, …]
  }

You may have to test and play around a bit to get it to match up perfectly, but sql_always_where gives you a bit more flexibility.