The very basics of data transfer are working:
 Exchange simple UTF8-Text with the standalone:
1a Get text from a textarea into a field of the standalone.
1b Set text of a textarea from a field of the standalone.
1c Run a LC script imported via the textarea (which loads text files)
 Exchange simple binary data (images) with the standalone:
2a Load an image from an <img> or <canvas> object into an image of the standalone.
2b Set an image of the standalone as source of an <img> or <canvas> object.
[I made a demo standalone, see "Succesful tests".]
There are some new bugs with editing text in the HTML 5 standalone (see the listing with the standalone), but there is already a 'flaw' workaround: Simply use the textarea and import the text to the field . The way back, exporting the imported UTF-8, shows again encoding problems .
So, for the original post, one has simply to solve the external to local problems for upload from and download to the current page. This will certainly be doable, as we can use newest HTML5: The standalone needs latest browser versions anyway.
For a few details to the technique used see "Successful tests" (link at top).
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