SO I've got a huge heap of ogged classical music on my iPod: this has
both composer and (often) artist tags (where `artist' == `performer').

I've *also* got a huge heap of mostly-ogged, partially-mp3ed
non-classical music (mostly jazz) which has only artist tags (some of
these are ID3v1 so can't do composer at all: for others, composer ==
artist so I used artist).

Now in order for the tag database to be of much use here, I need to
smush the value of artist into composer for all files that don't have a
composer tag. I was hoping that there was a notation for this, say
something like

%format "fmt_mostplayed" "(%3d) %s - %s" playcount composer:-artist title %sort = "inverse" %limit = "100"

"Composer" -> composer:-artist ? composer:-artist ~ "" -> album -> title = "fmt_title"

but alas there doesn't seem to be, and the .idx structure militates
against it: you'd have to make all those decisions *when the .idx was
generated*, rather than at rendering time.

Is my supposition right? Is there no way to do this? Will I have to
engage in a mega-retagging, or insert a truly ugly hardwired kludge that
copies `artist' to `composer' iff there is no composer, at tagdb build
time?

-- 
`He accused the FSF of being "something of a hypocrit", which
 shows that he neither understands hypocrisy nor can spell.'
   --- jimmybgood