Possibility to reuse server side helper functions in PUG before switching to Helix?

Until we switch to Helix it would be helpful to be able to put the server-side helper functions for all PUG forms in a separate file to avoid redundancy and versioning problems.

I try putting a function in a helper file (in a mixin):

//_helper.pug
// A mixin to inject server side helper functions in a block
mixin helpers()
	-
		function greet({ name }) {
			const result = typeof name === "string" ? `Hello, ${name}!` : "Hello, stranger!"
			return result
		}

and to import it, but without success:

//test.pug
extends ../views/form/default-form

block formContent
	//include ../forms/_helpers.pug
	//GIVES no such file or directory, open 'templates/forms/_helpers.pug'
	
	//include ../../forms/_helpers.pug
	//GIVES no such file or directory, open 'forms/_helpers.pug'
	
	//include ../../../forms/_helpers.pug
	//GIVES no such file or directory, open '../forms/_helpers.pug'

	//Assume the name of my root folder in the full Onify folder structure is 'app'
	include ../../app/forms/_helpers.pug
	//GIVES no such file or directory, open 'app/forms/_helpers.pug'
	
	+helpers()

	-
		const message = greet({ name: 'Test' })
	p= message

Possibly because i do not know the name in Onify for my root, or it could be that this is impossible anyway without the PUG basedir option set, which i can not access.

Is there a quickfix here which I'm missing?