[Seaside] How to set the filename of a returned document?

[Ian Prince]

My application returns pdf files with:

MyComponent>>renderContentOn: html
	html anchorWithDocument: contents
				mimeType: 'application/pdf'
				text: 'download'.

The pdf  files returned have names based on the session ids, e.g. 
@kMhhyhwLYiKxjcRl

How can I go about  setting the filename of the returned document to 
something else, such as "generated_document.pdf"?

Thanks,

Ian.