You can do this as a text field with a custom template. See https://code.google.com/p/wordpress-custom-content-type-manager/wiki/CustomizingManagerHTML
Say for example your custom field is named “password”. Copy the wp-content/plugins/custom-content-type-manager/tpls/fields/elements/_text.tpl
into wp-content/uploads/cctm/tpls/fields/elements/password.tpl
(the name must match the field name). In your copy, just change the field type from “text” to “password”:
<input type="password" name="[+name_prefix+][+name+]" class="cctm_text [+class+]" id="[+id_prefix+][+id+]" value="[+value+]" [+extra+]/>
Finally, you would need to flush the CCTM’s cache so it loads your custom template to draw those fields. Just go to the CCTM –> Clear Cache menu and you should be set.