Include Product Code into Inquiry Form?

Hi folks, 

I need to pre-populate a customer inquiry form with the {tag_productcode} on the Online Shop > Individual Product -Large template so that when a customer askes about that particular item, whe know which item the customer is asking about.

I' tried to add the tag to the value field but it erases when I use the properties panel:

<td><label for="CAT_Custom_391201">Item Number</label><br />

                <input type="text" maxlength="4000" name="CAT_Custom_391201" id="CAT_Custom_391201" class="cat_textbox" /></td>

Is there a safe way to add the tag ?