Just to follow up on this, I have resolved my issue by adding the field I was looking for into the mod_cmc.xml in the following place and editing mod_cmc.php
[site root]\modules\mod_cmc\mod_cmc.xml
[site root]\modules\mod_cmc\mod_cmc.php
In mod_cmc.xml I added the following at the start of the <fieldset name="advanced"> node :
<field name="layout"
type="modulelayout"
label="JFIELD_ALT_LAYOUT_LABEL"
description="JFIELD_ALT_MODULE_LAYOUT_DESC"/>
<field name="moduleclass_sfx" type="text" label="COM_MODULES_FIELD_MODULECLASS_SFX_LABEL"
description="COM_MODULES_FIELD_MODULECLASS_SFX_DESC"/>
And in mod_cmc.php I added the following at line 20 - 21 (commented out the original line) :
//$layout = 'default';
$layout = $params->get('layout', 'default');
This will add the the "Alternative field" dropdown onto the modules advanced tab.
@Daniel, any chance this could be added to the next release?
Thanks again for a great plugin,
Dan