How do I use a latexmkrc file to allow a standalone document to find the file

I am using LaTex in Overleaf to write my Thesis Proposal and eventually the Disseration. I thought it would be good to have all of these documents (and their presentations) in one project so I wouldn’t have to keep duplicating projects and can easily share files.

The proposal PAPER is currently the “default document” in the Overleaf project. I have a pretty extensive file structure to keep things organized, including “common” package and preamble files for papers and beamer presentations.

The proposal PRESENTATION is a stand alone document. Bottom line, Overleaf can’t seem to find the preamble/package documents for the stand alone document.

A little searching led to the use of a latexmkrc to convince the default document to search there first for my custom preambles and such.

However, I cannot figure out how to get my standalone beamer presentation to look at the latexmkrc file before trying to compile as a standalone.

Here’s my attempt at showing the code:

In the default document (in the main Overleaf file structure) the following works and finds my style files:

documentclass[11pt]{article}
usepackage{import}

usepackage[usenames,dvipsnames,table]{xcolor}

% Preamble
usepackage{preamble}

In the standalone file (which is in its own folder) the following does not work:

documentclass[xcolor = {usenames,dvipsnames,table},beamer]{standalone}

usepackage{import}

% Preamble
usepackage{beamer_preamble}

preamble and beamer_preamble are both .sty files which reside in a folder called “custom” which is in a folder called “support”. My latexmkrc file has the following code:

$ENV{'TEXINPUTS'}='./support/custom//:' . $ENV{'TEXINPUTS'}; 

Does anyone know how to get an Overleaf standalone file to check the latexmkrc file before compiling?