Excel com server with simulink

I have written some excel COM server code that runs successfully on MATLAB. I am now implementing it in Simulink, virtually trying to use simulink matlab function blocks to write/read data from specific spreadsheets. But when I run the same code on Simulink, I get a

Undefined function or variable 'exl'.

exl is of course the handle for the COM server. The exact same code works fine running from matlab. Just in case, I initially create the com server outside simulink, so the handle and the server are open once the simulink matlab function block runs.

The entire code is the following:

%% Activate specific sheet (Runs on MATLAB first)
exlSheets = exl.ActiveWorkbook.Sheets;
exlBiotreater = exlSheets.get('Item','Biotreater');
exlBiotreater.Activate
%% Create influent from signal (Rest of code in Simulink MATLAB function block)
bio1feed = influent
%% Write to specified range, calculate and read back.
exlActivesheetRange = get(exl.Activesheet,'Range','C5:C26');
exlActivesheetRange.Value = bio1feed;

if ~isempty(recycle)
    exlActivesheetRange = get(exl.Activesheet,'Range','D5:D26');
    exlActivesheetRange.Value = recycle;
end

exlBiotreater.Calculate

exlBiotreaterEFfluent = get(exl.Activesheet,'Range','J5:J26');
effluent = exlBiotreaterEFfluent.Value;
effluent = reshape([effluent{:}],size(effluent));

exlBiotreaterSludge = get(exl.Activesheet,'Range','K5:K26');
sludge = exlBiotreaterSludge.Value;
sludge = reshape([sludge{:}],size(sludge));