I have been trying to find a easiest way. But you don't know PHP... It's hard. Give you a suggestion.
Show the block "d3forum_block_list_forum" to your d3forum.
Edit "d3forum_main_listcategories.html" and remove some part you don't need.
Edit the block "d3forum_block_list_forum" to show this block only when $_SERVER['REQUEST_URI'] match to your required URI. Or you can edit theme and implement "$xoops_requesturi".
That's all what I can help you.
Others may help you with better and easier way.
Good luck