Workaround

Here is a workaround that someone else came up with to achieve this. Not sure of the ramifications, but the code may or may not help.

settings.php

<?php
//add folders in which the subsites reside to this array
$sites = array(
  'museum1',
  'museum2',
  'museum3',
);
$request = explode('/', trim($_SERVER['REQUEST_URI'], '/'));
if(sizeof($request) && preg_match('/^'.implode('|', $sites).'$/i', $request[0], $matches)) {
  // set the appropriate HTTP_HOST to trick Domain Access
  $site = $matches[0];
  $_SERVER['ORIGINAL_HTTP_HOST'] = $_SERVER['HTTP_HOST'];
  $_SERVER['HTTP_HOST'] = $site.'.'.$_SERVER['HTTP_HOST'];

  //rebuild the Q
  if(!empty($_GET['q'])) {
    $q = implode('/', $request);
    if(($pos = strpos($q, '?')) !== FALSE) {
      $q = substr($q, 0, $pos);
    }

    $size = strlen($site);
    $_GET['q'] = ltrim(substr($q, $size), '/');
    $HTTP_GET_VARS['q'] = $q;
  }

  //used to set the correct $base_url in settings.php
  global $da_site;
  $da_site = $site;
}

?>