Groovy GString template engine use default engine - jenkins

Question

I have a Jenkins shared library.
I'm loading a groovy resource file which looks like this:
return [${Constants.nodeIP}#${Constants.username}]
The Constants class:
public class Constants{
public static String nodeIP = "10.0.0.1"
public static String username = "barel"
}
My purpose is to load the resource file into String and also subtitute the $ signs with the actual value.
import Constants
def template = libraryResource resource: 'myTemplate.txt'
def finalResult = """
more text goes here
$template
and here
"""
println(finalResult)
Expected output is:
more text goes here
return [10.0.0.1#barel]
and here
But I'm getting:
more text goes here
return [${Constants.nodeIP}#${Constants.username}]
and here
The main point is that i need to pass the template through the template engine in order to substitute the values but for that I need to create an implicit mapping object and provide it to the template:
def engine=new groovy.text.SimpleTemplateEngine()
def templateEngine = engine.createTemplate(template)
def binding = [ "nodeIP" : "10.0.0.1", "username" : "barel"]
templateEngine.make(binding)
I don't want to re-declare all fields when I'm using the template.
Is there any way to get a reference to the defaultive/built-in TemplateEngine which already has access to all project fields and properties?