Sturmey Archer SRF5W lateral axle adjustment
Hmmm, I think I may be able to answer my own question with a negative.   After browsing some more I found Aaron Goss's post about stripping down a very similar hub.  The axle has a raised portion in the center which would prevent lateral movement.....  

I'm going to have to figure out something else.

Perhaps just sourcing a longer axle.
EDIT: Unfortunately I have the longest axle available (see p.56 of S.A. catalogue 2012-2013, which indicates 175mm is max axle length)

Alternatively having a framebuilder cut the dropouts off and replacing them with something saner.

EDIT: Or perhaps bodging up a replacement for the fulcrum arm with it's integrated locating washer ( HSJ905 on p.41 of catalogue).