I have had a look on the marketplace and have found a hook which is what I think you're looking for, removes the quote and multi-quote button from the first post. I have gone ahead and uploaded it to webflake for you. http://webflake.sx/files/file/1397-hide-quote-button-from-first-post/ I will upload this to WebFlake when I get home.
Alternatively I have found this from another site - I don't take any credit for the coding below.
Go to ACP ---> Look&Feel ---> *your skin* ---> Topic View ---> topicViewTemplate
Find: <a href="{parse url="module=post&section=post&do=reply_post&f={$this->request['f']}&t={$this->request['t']}&qpid={$post['post']['pid']}" base="publicWithApp"}" title="{$this->lang->words['quote_with_mq']}">{parse replacement="mq_post_icon"} {$this->lang->words['mq']}</a>Before, Add: <if test="isFirst:|:!$post['post']['new_topic']">Find: <if test="canEdit:|:$post['post']['_can_edit'] === TRUE">Before, Add: </if>Save and repeat for each skin.