There is no option for that.
You will have to change the code:
$html = '<a title="'.$alt.'" class="hikashop_image_small_link" rel="{handler: \'image\'}" href="'.$this->uploadFolder_url.$path.'" onclick="SqueezeBox.fromElement(this,{parse: \'rel\'});return false;" target="_blank" onmouseover="return hikashopChangeImage(\''.$addpopup.'\',\''.$this->uploadFolder_url_thumb.'\',\''.$this->thumbnail_x.'\',\''.$this->thumbnail_y.'\',this,\''.$alt.'\');" '.$optionslink.'>'.$html.'</a>';
to:
$html = '<a title="'.$alt.'" class="hikashop_image_small_link" rel="{handler: \'image\'}" href="'.$this->uploadFolder_url.$path.'" onclick="return hikashopChangeImage(\''.$addpopup.'\',\''.$this->uploadFolder_url_thumb.'\',\''.$this->thumbnail_x.'\',\''.$this->thumbnail_y.'\',this,\''.$alt.'\');" '.$optionslink.'>'.$html.'</a>';
in the file administrator/components/com_hikashop/helpers/image.php