Hi
Couldn't find such an option.

As '&' gets transformed to & in a post and screws the URL I made a Free HTML widget for the sidebar

See http://calstock.org.uk/elf.php

<form action="http://yourdomian.##/###.php">
<div>
<label>1 to 19&nbsp;</label>
<input type="hidden" id="disp" name="disp" value="posts">
<input type="number" style="width:3em" id="posts" name="posts" type="text" size="1" value="" min="1" max="19" />
<input type="submit" value="Go">
</div>
</form>

Only get the full posts when it's the value set in the back office, else it's excerpts.

Still to do one for comments on each post.