Compatibility with context module

With above patch in place and the one included in the next comment, you can just use the tpl.php file provided by context called "context-block-editable-region.tpl.php" and override it with someting like:

<?php foreach ($blocks as $block): ?>
<?php 
$esi_config = _esi__block_settings($block->module, $block->delta);
?>
<?php if ($esi_config->enabled == 1) : ?>
  <?php print theme('esi_tag', $block); ?>
<?php else : ?>
  <?php print theme('block', $block); ?>
<?php endif; ?>
<?php endforeach; ?>

In addition you also need to patch esi.inc which handles the request for the block content. Otherwise the core block_list will provide an empty array because block placement is handled by context.

Not sure if this is the best way to do this, but it worked for me...

patch mentioned in #2. Should be used together with patch in #1.