Expose option does not work when requiring streams.

I'm having trouble getting Browserify to respect the `expose` option if I pipe a stream into it.

For example:

``` javascript
var browserify = require('browserify');
browserify().require(fs.createReadStream('./bar.js'), { basedir: '.' expose: 'bar'})
```

The contents of the file are included, however no module name is exposed. Am I doing something wrong here?
