How can I use special character in Liquid Filter?

[mcpol]

SITUATION

I have parameter and filter and this is  the LOOKML:

parameter: attr {
   type: unquoted
   description: "Name of the event attribute for condition 3."
}

filter: string_val {
  type: string
  description: "String value of the event attribute for condition 3."
}

The value of those are as follows:

attr = 'page_name'

string_val = 'home/$(pages)/name'

However, the generated SQL by Looker is: 

WHERE page_name = ‘home/pages/name’

For some reason, looker is not generating the special characters in the value.

ATTEMPT #1

The parameter and filter is being utilized in derived table within the LookML as:

 AND {% condition string_val %}
      {% parameter attr %}
      {% endcondition %}

Then the attempt to solve the issue is to use the url_encode which I found somewhere in this site.
 

 AND {% condition string_val | URL_ENCODE %}
      {% parameter attr %}
      {% endcondition %}

But it's not working. The special characters in the value are still not showing in the generated SQL.

ATTEMPT #2

After that attempt, I tried to create another parameter and use type: unquoted

{% if unquoted_val._parameter_value == blank %}
{% else %}
AND {% parameter attr %} = '{% parameter unquoted_val | escape %}'
{% endif %}

parameter: unquoted_val {
  type: unquoted
  description: "Unquoted value of the event attribute for condition 2."
}

parameter: attr {
  type: unquoted
  description: "Name of the event attribute for condition 3."
}

However, I’m getting an error because unquoted parameters only contain underscore, numbers, letters, “.” and “$”.

The use case is a bit unusual and there’s no article about this. Hoping someone can help me. Thanks!