Common keys on separate lattice plots

In 'normal' plotting, by using text(.... outer = TRUE), I can set a
title that can refer to multiple plots.

I'm trying to achieve a similar effect with several trellis objects
with which I wish to use a common key.  I can only think of
complicated ways of achieving such an end by using a separate grid
graphic which didn't have any plot, but text only.

Is there something more elegant?

best

Patrick Connolly
HortResearch
Mt Albert
Auckland
New Zealand 
Ph: +64-9 815 4200 x 7188
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