Searching by post formats

Having some difficulty coming up with a method for searching by “post formats“.

I’ve successfully implemented some code that uses the wp_dropdown_categories function to allow searches to be filtered by category and taxonomy via drop down selectors.

But I’m a bit stuck on how to add filtering for post formats.

Does anyone have a method for doing this that doesn’t involve creating a redundant, tag, category or taxonomy to mirror post_format types for use in the wp_dropdown_categories ‘taxonomy’ argument?

Thanks in advance.

Here is where I’m at:

<fieldset>
<label>Keywords</label>
<input type="text" class="search form-text" name="s" id="s" value="<?php echo trim( get_search_query() ); ?>" placeholder="Type keywords here" />
</fieldset>

<fieldset>
<label>Category</label>
<div class="styled-select">
<div class="icon"></div>
<?php wp_dropdown_categories('&show_option_none=All&&hide_empty=0'); ?>
</div>
</fieldset>

<fieldset>
<label>My Taxonomy</label>
<div class="styled-select">
<div class="icon"></div>
<?php wp_dropdown_categories(array('taxonomy'=> 'MyTaxonomy','hide_empty' => 0, 'show_option_none' => 'All')); ?>
</div>
</fieldset>

<fieldset class="submit">
<input type="submit" class="submit button btn-blue" name="submit" id="searchsubmit" value="Search"/>
</fieldset>
</form>

This is what I wish existed:

<fieldset>
<label>Post Format</label>
<div class="styled-select">
<div class="icon"></div>
<?php wp_dropdown_post_format('&show_option_none=All&&hide_empty=0'); ?>
</div>
</fieldset>