{module_categorylist} Categories drop down show sub categories only

Question

Hi
On this page I have a FAQ search at the top of the page.
http://www.pantheraaccounting.co.uk/features/faqs
In the ‘Categories’ drop down I have a set of sub Categories called ‘FAQ’ - is there anyway I can just show the subset of categories instead of showing All Categories I have created for other parts of the site.
e.g. Drop down list to show only
FAQ
- Corporation Tax
- Self Assessment
- UTR
- Xero
The code for this is   
<table class="faq-search" cellspacing="0" cellpadding="2" border="0">
                <tbody>
                    <tr>
                        <td><label for="CAT_Category">Category</label><br />
                        <select class="cat_dropdown_small" id="CAT_Category" name="CAT_Category">{module_categorylist}</select></td>
                        <td><label for="CAT_FAQSearch">Search (Optional)</label><br />
                        <input class="cat_textbox_small" type="text" id="CAT_FAQSearch" name="CAT_FAQSearch" /></td>
                        <td> <br />
                        <input class="cat_button" type="submit" value="Search" /></td>
                    </tr>
                </tbody>
            </table>

Answer 1

I have found the answer on another forum post - thank you to Adam (Logo Pogo)  https://forums.adobe.com/message/5818145#5818145
If anyone else is looking for a solution this works;
Actually, there is an undocumented way of doing this. Just like with the ecommerce catelogue list dump you can use the ID of the catalogue / category in the module tag to render that level like so:
Ecommerce catalogue list dump:
{module_cataloguelistdump,-1} --- renders all catalogues
{module_cataloguelistdump,12345} --- renders the catalogue level with this ID of the top catalogue
System Categories list:
{module_categorylist} --- renders all categories
{module_categorylist,12345} --- renders the category level with this ID of the top category