If you are comfortable with changing source code you can try:
In file ‘search-types-custom-fields-widget.php’ change line 1041 from:
$and_or = $_REQUEST['search_types_custom_fields_and_or'] == 'and' ? 'AND' : 'OR';
to:
#$and_or = $_REQUEST['search_types_custom_fields_and_or'] == 'and' ? 'AND' : 'OR';
$and_or = 'OR';
This forces the search condition to ANY.
change lines 125-131 from:
<div style="text-align:center;margin:10px;">
Results should satisfy<br>
<input type="radio" name="search_types_custom_fields_and_or" value="and" checked><strong>All</strong>
<input type="radio" name="search_types_custom_fields_and_or" value="or"><strong>Any</strong></br>
of the search conditions.
</div>
to:
<!--
<div style="text-align:center;margin:10px;">
Results should satisfy<br>
<input type="radio" name="search_types_custom_fields_and_or" value="and" checked><strong>All</strong>
<input type="radio" name="search_types_custom_fields_and_or" value="or"><strong>Any</strong></br>
of the search conditions.
</div>
-->
That should keep the and or box from being generated.
After looking at the code for this I saw some errors so I will be making a maintenance release soon and unfortunately you will need to again manually change these lines if you upgrade.