Overriding CSS class on custom block

Hello

I'm programmatically creating a block in a module and simply want to add a css class to the block wrapper. There seems to be some advice on how manipulate block classes in template preprocess functions, but I just want to be able to set it where I create the block. Is this possible?

This is what I have at the moment

function tp_core_block_info() {
    $blocks['myblock'] = array(
      'info' => t('My Block'),
      'cache' => DRUPAL_NO_CACHE,
    );
}

function mymodule_core_block_view($delta = '') {
    case 'myblock' :
	    $block['content'] = 'My Content';
    break;  
  }
  return $block;
}

This produces a block with the following html wrapper

<div id="block-my-module-my-block" class="block my-block content-region block-my-block block-my-module-my-block odd block-without-title">
*rest of block html here*

All I want to do is add a new class "no-background" to the class attribute at the time the block is created. I know this won't work, but I'm looking for something like this:

function tp_core_block_info() {
    $blocks['myblock'] = array(
      'info' => t('My Block'),
      'cache' => DRUPAL_NO_CACHE,
      'class' => 'no-background',
    );
}

The reason I want to do it this way is that for the most part, the blocks on my site will all have a white background, but in certain cases I want to turn this background off, so for these blocks I want to set a common css class that will disable it.

Is this possible?

I see that you can set a "properties" property in hook_block_info, but I don't see any information on what type of properties you can set or how.

Any help would be much appreciated!