OK, so no-one has ideas as per my question in elog:67088.

Looking at the issue from another angle.

If you attach a pdf file (for example), two files are added to the logbook:

../logbooks/hidden/110705_235520_whatthis-0.png
../logbooks/hidden/110705_235520_whatthis.pdf

Is there any way that you can select an attachent, but only the thumbnail (.png in this case) is stored (and
subsequently viewed)?  Options for ability to select an attachment, or how the thumbnail is manipulated/viewed
exist, but nothing about the storage or otherwise of the original document that I can find.

I've tried manually deleting the .pdf file (after going through the automatic routine to make an attachment),
and elog doesn't seem upset at the lack of the .pdf file at all.  The only time anything happens is if one
clicks on the image - and then you get a 'file not found' message from the browser - I could live with that.

In my case the original .pdf file is elsewhere, I've no need to have duplicates scatted in various logbooks, and
while ideally that would also be true of the thumbnail, it is fair enough for this to be stored in each logbook
where it is required.  This removes the issue of how to have an attachment in a different logbook (other than by
links, which would get rather tiresome to have to keep making).

Anyone any ideas?