How to pass multiple parameters to subtemplate on StringTemplate4

Question

I'm trying to call a subtemplate where I nedd to pass two expressions as parameter and deal with those parameter with a CustomRenderer.

When calling a subtemplate + CustomRenderer with one parameter it's done by calling a method from the template context as code below.

My question is: how can I call for example

$concat2values(context.Value, "Literal")$

given context.Value is a string "somevalue" and as a result receive

somevalueLiteral

obs.: my concerns are that the CustomRenderer just reveice one object paramater and in no try I could build the template this way. My aim is to intercep some processed code from script back on the "Engine" that process it.

templategroup.stg

group mygroup;

delimiters "$","$"

main(context) ::= <<
$formatSomething(context.Value)$
>>

formatSomething(value) ::= <<
$value; format = "_formatSomething_"$
>>

myformater.cs

using Antlr4.StringTemplate;
using System;
using System.Globalization;
using System.Linq;

namespace Engine.Components.Engine.Formatters
{
    public class SomeFormatter: StringRenderer
    {
        public override string ToString(object o, string formatString, CultureInfo culture)
        {
            if ("_formatSomething_".Equals(formatString))
                return FormatSomething(o);
            return base.ToString(o, formatString, culture);
        }

        private string FormatSomething(object o)
        {
            ** DO STUFF **
            string result = do_stuff_and_return_it_formatted();
            return result;
        }
    }
}

mytemplateengine.cs

private string ProcessTemplate<T>(string fullPathTemplateFileName, T context)
{
    try
    {
        var templateSource = File.ReadAllText(fullPathTemplateFileName);
        var groupTemplate = CreateTemplateGroup(templateSource);

        var templates = new TemplateGroupString(groupTemplate);
        // vvvvvvv----- SHOULD I USE OBJECT OR ANOTHER SPECIFIC TYPE TO THE TASK?
        templates.RegisterRenderer(typeof(object), new SomeFormatter());      
        var engine = templates.GetInstanceOf("main");

        if (engine == null)
            throw new Exception($"Failed to get template {fullPathTemplateFileName}");

        engine.Add("context", context);

        return engine.Render();
    }
    catch (Exception ex)
    {
        Errors.Add($"{ex.Message}{ex.StackTrace}");
        return $"{ex.Message}{ex.StackTrace}";
    }
}